As filed with the Securities and Exchange Commission on May 2, 2024

Registration No.     

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Aspen Aerogels, Inc.

(Exact name of registrant as specified in its charter)

Delaware	04-3559972
(State or other jurisdiction of incorporation or organization)	(I.R.S. Employer Identification No.)

30 Forbes Road, Building B

Northborough, Massachusetts 01532

(508) 691-1111

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Donald R. Young

President and Chief Executive Officer

30 Forbes Road, Building B

Northborough, Massachusetts 01532

(508) 691-1111

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copy to:

John T. Rudy, Esq.

Sahir Surmeli, Esq.

Nishant M. Dharia, Esq.

Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

One Financial Center

Boston, Massachusetts 02111

(617) 542-6000

Approximate date of commencement of proposed sale to the public:

From time to time or at one time after the effective date of this Registration Statement.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. ☐

If any of the securities being registered on this Form are being offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box ☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ☐

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer	☐	Accelerated filer	☒
Non-accelerated filer	☐	Smaller reporting company	☐
	☐	Emerging growth company	☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided Section 7(a)(2)(B) of the Securities Act. ☐

The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with section 8(a) of the Securities Act, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said section 8(a), may determine.

The information in this prospectus is not complete and may be changed without notice. The selling shareholder may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and the selling shareholder named in this prospectus is not soliciting offers to buy these securities in any state where the offer or sale of these securities is not permitted.

Subject to completion, dated May 2, 2024

PRELIMINARY PROSPECTUS

21,070,518 Shares of Common Stock

This prospectus relates to the offer and sale by the selling shareholder identified in this prospectus, and any of its pledgees, donees, transferees, or other successors in interest, of up to 21,070,518 shares of common stock of Aspen Aerogels, Inc., par value $0.00001 per share (the “Common Stock”), which consists of:

(i) up to 3,462,124 shares of Common Stock sold to Spring Creek Capital, LLC, an affiliate of the selling shareholder, pursuant to that certain securities purchase agreement, dated as of June 29, 2021 (the “2021 SPA”), which were subsequently transferred to the selling shareholder on May 2, 2022;

(ii) up to 5,290,092 shares of Common Stock issuable upon conversion of Convertible Senior PIK Toggle Notes due 2027 issued to the selling shareholder (the “Notes”), pursuant to that certain note purchase agreement, dated as of February 15, 2022 (the “2022 NPA”) and subsequently amended by an amendment to the Notes, dated as of November 28, 2022 (the “Notes Amendment”), or pursuant to any other term of the Notes, as amended by the Notes Amendment, including as a result of any of the payment-in-kind (“PIK”) provisions, based upon a conversion price of $29.936625 per share;

(iii) up to 1,791,986 shares of Common Stock sold to the selling shareholder pursuant to that certain securities purchase agreement, dated as of February 15, 2022 (the “2022 SPA”); and

(iv) up to 10,526,316 shares of Common Stock sold to the selling shareholder in connection with an underwritten public offering consummated in November 2022 (the “2022 Offering”).

This prospectus covers any additional securities that may become issuable by reason of stock splits, stock dividends or other similar transactions or as a result of PIK payments.

We are filing the registration statement of which this prospectus is a part at this time, in part, to fulfill contractual obligations to do so pursuant to the 2021 SPA, 2022 NPA, and 2022 SPA. We will not receive any of the proceeds from the sale of the Common Stock by the selling shareholder.

The selling shareholder and its pledgees, donees, transferees, or other successors in interest may offer the shares of Common Stock from time to time in one or more transactions at fixed prices, at prevailing market prices at the time of sale, at varying prices determined at the time of sale, at negotiated prices, or in trading markets for our Common Stock. Additional information on the selling shareholder, and the times and manner in which it may offer and sell shares of our Common Stock under this prospectus, is provided under “Selling Shareholder” and “Plan of Distribution” in this prospectus.

Our Common Stock is quoted on The New York Stock Exchange under the symbol “ASPN.” On May 1, 2024, the last reported sale price of our Common Stock was $15.22 per share.

Investing in our Common Stock involves certain risks. See “Risk Factors ” beginning on page 8 of this prospectus for the risks that you should consider. You should read this entire prospectus carefully before you make your investment decision.

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR DETERMINED IF THIS PROSPECTUS IS TRUTHFUL OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The date of this prospectus is      , 2024

TABLE OF CONTENTS

	Page
ABOUT THIS PROSPECTUS		1
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS		2
PROSPECTUS SUMMARY		4
RISK FACTORS		8
DESCRIPTION OF THE TRANSACTIONS		9
USE OF PROCEEDS		11
SELLING SHAREHOLDER		12
PLAN OF DISTRIBUTION		14
LEGAL MATTERS		17
EXPERTS		17
WHERE YOU CAN FIND MORE INFORMATION		17
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE		18

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ABOUT THIS PROSPECTUS

Except where the context requires otherwise, in this prospectus the terms “Company,” “our company,” “Aspen,” “we,” “us,” and “our” refer to Aspen Aerogels, Inc., a Delaware corporation, and, where appropriate, its direct and indirect subsidiaries.

You should rely only on the information contained or incorporated by reference in this prospectus. Neither we nor the selling shareholder have authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. For further information, please see the section of this prospectus entitled “Where You Can Find More Information.” The selling shareholder is not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted.

You should not assume that the information appearing in this prospectus is accurate as of any date other than the date on the front cover of this prospectus or that any information subsequently incorporated by reference in this prospectus is accurate as of any date subsequent to the date of the document so incorporated by reference, regardless of the time of delivery of this prospectus or any sale of a security. Our business, financial condition, results of operations, and prospects may have changed since those dates.

This prospectus contains trademarks, tradenames, service marks, and service names of the Company.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

The Securities and Exchange Commission, or SEC, encourages companies to disclose forward-looking information so that investors can better understand a company’s future prospects and make informed investment decisions. This prospectus contains such “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. These statements involve known and unknown risks, uncertainties and other important factors, which may cause our actual results, performance or achievements to be materially different from any future results, performances or achievements expressed or implied by the forward-looking statements. Forward-looking statements include, but are not limited to, statements about: the expected future growth of the market for our aerogel products and our continued gain in market share, in particular in the electric vehicle, or EV, market, the energy infrastructure insulation market, the lithium-ion battery thermal barrier markets, and other markets we target; our beliefs in the appropriateness of our assumptions, the accuracy of our estimates regarding expenses, loss contingencies, future revenues, revenue capacity, future profits, uses of cash, available credit, capital requirements, and the need for additional financing to operate our business and for capital expenditures and to fund our planned strategic business initiatives; the performance of our aerogel blankets; our expectation that we will be successful in obtaining, enforcing and defending our patents against competitors and that such patents are valid and enforceable; our expectations regarding the investment to open a second manufacturing facility in Georgia, the extended construction and commissioning timeframe for the planned second manufacturing facility, our efforts to manage the construction of the second plant to align with our expectations of demand from EV customers; our estimates of annual production capacity; beliefs about the commercial potential for our technology in the electric vehicle market; beliefs about our ability to produce and deliver products to electric vehicle customers; beliefs about Aspen’s contracts with the major automotive manufacturers; our expectations about the size and timing of awarded business in the electric vehicle market, future revenues and profit margins, arising from our supply relationship and contract with automotive OEMs and our ability to win more business and increase revenue in the electric vehicle market; beliefs about the performance of our thermal barrier products in the battery systems of electric vehicles; the current or future trends in the energy, energy infrastructure, chemical and refinery, LNG, sustainable building materials, electric vehicle thermal barrier, electric vehicle battery materials or other markets and the impact of these trends on our business; our investments in the electric vehicle market and aerogel technology platform; our beliefs about the financial metrics that are indicative of our core performance; our expectations about the effect of manufacturing capacity on financial metrics such as Adjusted EBITDA; our expectations about future revenues, expenses, gross profit, net loss, loss per share and Adjusted EBITDA, sources and uses of cash, capital requirements and the sufficiency of our existing cash balance and available credit; our beliefs about the outcome, effects or estimated costs of current or potential litigation or their respective timing, including expected legal expense in connection with our patent enforcement actions; our expectations about future material costs and manufacturing expenses as a percentage of revenue, including the impact of engaging one or more contract manufacturers in China for supply of our energy industrial products; our expectation about the ability of the Chinese contract manufacturers that we engage to consistently supply the aerogel product that we order in a timely manner; our expectations of future gross profit and the effect of manufacturing expenses, manufacturing capacity and productivity on gross profit; our expectations about our resources and other investments in new technology and related research and development activities and associated expenses; our expectations about short and long term (a) research and development (b) general and administrative and (c) sales and marketing expenses; our expectations of revenue growth, increased gross profit, and improving cash flows over the long term; our intentions about managing capital expenditures and working capital balances; and our expectations about potential sources of future financing.

Words such as “may,” “will,” “anticipate,” “estimate,” “expects,” “projects,” “intends,” “plans,” “believes” and words and terms of similar substance used in connection with any discussion of future operating or financial performance, identify forward-looking statements. All forward-looking statements are management’s present expectations of future events and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those described in the forward-looking statements. These risks include,

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but are not limited to, those under the heading “Risk Factors” contained in Item 1A of our Annual Report, as may be updated or supplemented by subsequent filings that we make with the SEC.

In light of these assumptions, risks and uncertainties, the results and events discussed in the forward-looking statements contained in this prospectus might not occur. Shareholders and other readers are cautioned not to place undue reliance on the forward-looking statements, which speak only as of the date of this prospectus. We are not under any obligation, and we expressly disclaim any obligation, to update or alter any forward-looking statements, whether as a result of new information, future events or otherwise. All subsequent forward-looking statements attributable to Aspen Aerogels, Inc. or to any person acting on its behalf are expressly qualified in their entirety by the cautionary statements contained or referred to in this section.

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PROSPECTUS SUMMARY

This prospectus summary highlights important features of the potential offers and sales that the selling shareholder may undertake from time to time and the information included or incorporated by reference in this prospectus. Because it is a summary, it may not contain all of the information that may be important to you. You should carefully read this entire prospectus, including the section entitled “Risk Factors.”

Overview of Aspen

We are an aerogel technology company that designs, develops and manufactures innovative, high-performance aerogel materials used primarily in the energy industrial, sustainable insulation materials and EV markets. We have provided high-performance aerogel insulation to the energy industrial and sustainable insulation markets for nearly two decades. We have developed and commercialized our proprietary line of PyroThin^® aerogel thermal barriers for use in battery packs in EVs. In addition, we are developing applications for our aerogel technology in the battery materials market and a number of other high-potential markets. Our core businesses are organized into two reportable segments: Energy Industrial and Thermal Barrier. The following describes our key product offerings and new product innovations by reportable segment.

Products

Our core businesses are organized into two reportable segments: Energy Industrial and Thermal Barrier. The following describes our key product offerings and new product innovations by reportable segment.

Energy Industrial

We design, develop and manufacture innovative, high-performance aerogel insulation used primarily in the energy industrial and sustainable insulation materials markets. We believe our aerogel blankets deliver the best thermal performance of any widely used insulation product available on the market today and provide a combination of performance attributes unmatched by traditional insulation materials. Our end-user customers select our products where thermal performance is critical and to save money, improve resource efficiency, enhance sustainability, preserve operating assets and protect workers. Our insulation is used by oil producers and the owners and operators of refineries, petrochemical plants, LNG facilities, power generating assets and other energy industrial companies. Our Pyrogel^® and Cryogel^® product lines have undergone rigorous technical validation by industry leading end-users and achieved significant market adoption.

We also derive revenue from a number of other end markets. Customers in these markets use our products for applications as diverse as military and commercial aircraft, trains, buses, appliances, apparel, footwear and outdoor gear. As we continue to enhance our Aerogel Technology Platform, we believe we will have additional opportunities to address high-value applications in the global insulation market, and in a number of new, high-value markets, including hydrogen energy, filtration, water purification, and gas sorption.

We market and sell our products primarily through a sales force based in North America, Europe and Asia. The efforts of our sales force are supported by a small number of sales consultants with extensive knowledge of a particular market or region. Our sales force is responsible for establishing and maintaining customer and partner relationships, delivering highly technical information and ensuring high-quality customer service.

Our salespeople work directly with end-user customers and engineering firms to promote the qualification, specification and acceptance of our aerogel and thermal barrier products. We also rely on an existing and well-established channel of qualified insulation distributors and contractors in more than 50 countries around the world to ensure rapid delivery of our aerogel products and strong end-user support.

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Thermal Barrier

We are also actively developing a number of promising aerogel products and technologies for the electric vehicle (“EV”) market. We have developed and are commercializing our proprietary line of PyroThin^® aerogel thermal barriers for use in battery packs in EVs. Our PyroThin product is an ultra-thin, lightweight and flexible thermal barrier designed with other functional layers to impede the propagation of thermal runaway across multiple lithium-ion battery system architectures. Our thermal barrier technology is designed to offer a unique combination of thermal management, mechanical performance and fire protection properties. These properties enable EV manufacturers to achieve critical battery performance and safety goals. In addition, we are seeking to leverage our patented carbon aerogel technology to develop industry-leading battery materials for use in lithium-ion battery cells. These battery materials have the potential to increase the energy density of the battery cells, thus enabling an increase in the driving range of EVs.

The commercial potential for our PyroThin thermal barriers and our carbon aerogel battery materials in the EV market is significant. Accordingly, we are hiring additional personnel, incurring additional operating expenses, incurring significant capital expenditures to expand aerogel manufacturing capacity, establishing an automated thermal barrier fabrication operation, enhancing research and development resources and expanding our battery material research facilities, among other items.

We have entered into production contracts with certain major OEMs, including General Motors LLC (“GM”) to supply fabricated, multi-part thermal barriers for use in the battery system of its next-generation EVs. Pursuant to the contracts with GM, we are obligated to supply the barriers at fixed annual prices and at volumes to be specified by the customer up to a daily maximum quantity through the term of the agreements, which expire at various times from 2026 through 2034. While GM has agreed to purchase its requirement for the barriers from us at locations to be designated from time to time, it has no obligation to purchase any minimum quantity of barriers under the contracts. In addition, GM may terminate the contracts any time and for any or no reason. All other terms of the contracts are generally consistent with GM’s standard purchase terms, including quality and warranty provisions customary in the automotive industry. We have also entered into production contracts with Toyota, Scania, Audi, a luxury brand of the Volkswagen Group, and ACC, a battery cell joint venture between Stellantis N.V, Saft-TotalEnergies and Mercedes-Benz.

Manufacturing Operations

We manufacture our products using our proprietary technology at our facility in East Providence, Rhode Island. We have operated the East Providence facility since 2008 and have increased our capacity in phases. To meet expected growth in demand for our aerogel products in the EV market, we have been in the process of expanding our aerogel blanket capacity by constructing a second manufacturing plant in Bulloch County, Georgia. However, in order to manage the development of the second plant so that its increased capacity comes online in a manner that aligns with our current expectations as to demand from our EV customers, we are extending the timeframe for construction and commissioning of the second plant until such time as its capacity is supported by increased demand. In the meantime, and until we ramp up construction, we expect to be able to substantially reduce our planned capital expenditures for 2024. At the same time, we believe that productivity improvements in our existing Rhode Island facility combined with the supplemental supply of our energy industrial products from one or more external manufacturing facilities in China will permit us to achieve a target revenue capacity of approximately $650 million in 2024 and prior to the completion and start-up of the second plant. Nonetheless, there can be no assurance as to when we will ramp up construction on the second plant. There can also be no assurance that our contract manufacturing strategy of meeting the demand of our energy industrial customers with supply from one or more external manufacturing facilities in China will provide us with adequate manufacturing capacity or supply for that expected demand. Furthermore, when we ramp up construction on the second plant, further cost inflation and/or supply chain disruptions, as well as potential changes in the scope of

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the facilities, could lead to increases to our prior estimated costs for completion of the second plant. In 2023, we opened our 59,000-square-foot engineering and rapid prototyping facility in Marlborough, MA. Our Advanced Thermal Barrier Center (ATBC) is designed to be the engineering hub of PyroThin cell-to-cell barriers, which help manufacturers optimize the safety and performance of battery packs for eMobility and energy storage system (ESS) markets.

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The Offering

Shares of Common Stock that may be offered by the selling shareholder Up to 21,070,518 shares, including (i) 3,462,124 shares issued to Spring Creek Capital, LLC, an affiliate of the selling shareholder, pursuant to the 2021 SPA, which were subsequently transferred to the selling shareholder on May 2, 2022; (ii) up to 5,290,092 shares issuable upon conversion of the Notes, as amended by the Notes Amendment, or pursuant to any other term of the Notes, as amended by the Notes Amendment, including as a result of any of the PIK provisions, based upon a reduced conversion price of $29.936625 per share; (iii) 1,791,986 shares issued to the selling shareholder pursuant to the 2022 SPA; and (iv) 10,526,316 shares issued to the selling shareholder in connection with the 2022 Offering.

Use of proceeds We will not receive any proceeds from the sale of shares of Common Stock in this offering. See the section entitled “Use of Proceeds.”

New York Stock Exchange symbol ASPN

Risk factors You should consider carefully the information set forth in the section entitled “Risk Factors,” beginning on page 8 of this prospectus, in deciding whether or not to invest in our Common Stock.

Plan of distribution The selling shareholder and its pledgees, donees, transferees, or other successors in interest may offer the shares of Common Stock from time to time in one or more transactions at fixed prices, at prevailing market prices at the time of sale, at varying prices determined at the time of sale, at negotiated prices, or in trading markets for our Common Stock. See the section entitled “Plan of Distribution” beginning on page 14 of this prospectus for a complete description of the manner in which the shares registered hereby may be distributed.

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RISK FACTORS

An investment in our securities involves a high degree of risk. Before making an investment decision you should carefully read and consider the risks and uncertainties and all of the other information, documents or reports included or incorporated by reference in this prospectus, including, without limitation, the risk factors in the section entitled “Risk Factors” in our most recent Annual Report on Form 10-K, which is on file with the SEC, as updated by our subsequent filings with the SEC under the Exchange Act. If any of the risks set forth in our most recent Annual Report on Form 10-K or subsequent Exchange Act reports actually occur, our business, financial condition, and/or results of operations could suffer. In that case, the market price of our Common Stock offered by this prospectus could decline, and you may lose all or part of your investment. You should read the section entitled “Special Note Regarding Forward-Looking Statements” above for a discussion of what types of statements are forward-looking statements, as well as the significance of such statements in the context of this prospectus. Additional risks and uncertainties that we do not presently know or that we currently deem immaterial may also have a material adverse effect on our business.

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DESCRIPTION OF THE TRANSACTIONS

2021 Securities Purchase Agreement

On June 29, 2021, we entered into a securities purchase agreement (the “2021 SPA”) with Spring Creek Capital, LLC (“Spring Creek”), an affiliate of Koch Disruptive Technologies, LLC. Pursuant to the terms of the 2021 SPA, we sold and issued to Spring Creek an aggregate of 3,462,124 shares of Common Stock (the “2021 Shares”) at a purchase price equal to $21.663 per share, for aggregate gross proceeds of approximately $75.0 million (the “2021 Private Placement”). The 2021 Private Placement closed on June 30, 2021.

The 2021 SPA required us to prepare and file a registration statement with the U.S. Securities and Exchange Commission (the “SEC”) within 75 days of the closing of the 2021 Private Placement to register the resale of the 2021 Shares, and to use commercially reasonable efforts to have such registration statement declared effective within 30 days following the filing of the registration statement if there is no review by the SEC, or within 120 days following the filing of the registration statement in the event of such a review.

The 2021 SPA contains customary representations, registration rights, warranties and agreements by us, customary conditions to closing, indemnification obligations by us, including for liabilities under the Securities Act of 1933, as amended (the “Securities Act”), termination provisions, and other obligations and rights of the parties. The representations, warranties and covenants contained in the 2021 SPA were made only for purposes of such agreement and as of specific dates, were solely for the benefit of the parties to such agreement, and may be subject to limitations agreed upon by the contracting parties.

In connection with the 2021 Private Placement, we paid Nomura Greentech Capital Advisors Securities, LLC a financial advisory fee of $1,312,500.

Pursuant to the 2021 SPA, we filed a registration statement on Form S-3 (File No. 333-259449) with the SEC on September 10, 2021 to register the 2021 Shares (the “2021 Registration Statement”), which was declared effective on September 20, 2021.

On May 2, 2022, Spring Creek transferred the 2021 Shares to Wood River Capital, LLC (the “selling shareholder”), an affiliate of Koch Disruptive Technologies, LLC.

2022 Purchase Agreements

On February 15, 2022, we entered into a securities purchase agreement (the “2022 SPA”) and a note purchase agreement with the selling shareholder (the “2022 NPA” and together with the 2022 SPA, the “2022 Purchase Agreements”).

Pursuant to the terms of the 2022 SPA, we sold and issued to the selling shareholder an aggregate of 1,791,986 shares of Common Stock at a purchase price equal to $27.902 per share, for aggregate gross proceeds of approximately $50.0 million (the “2022 Common Stock Private Placement”). The 2022 Common Stock Private Placement closed on March 28, 2022.

Pursuant to the terms of the 2022 NPA, we agreed to sell to the selling shareholder $100,000,000 in aggregate principal amount of the Notes, convertible into shares of Common Stock (the “2022 Convertible Note Private Placement”). The 2022 Convertible Note Private Placement closed on February 18, 2022 and the Notes were issued on such date.

The Notes are governed by a form of indenture (the “Indenture”) incorporated by reference into the Notes. The Notes bear interest at the Secured Overnight Financing Rate (“SOFR”) plus 5.50% per annum if interest is paid in cash (“Cash Interest”), or, if interest is paid in kind (through an increase in the principal amount of the

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outstanding Notes or through the issuance of additional Notes), at SOFR plus 6.50% per annum (“PIK Interest”). Under the terms of the investment, SOFR has a floor of 1% and a cap of 3%. We can elect to make any interest payment through Cash Interest, PIK Interest or any combination thereof. Interest on the Notes is payable semi-annually in arrears on June 30 and December 30, commencing on June 30, 2022. It is expected that the Notes will mature on February 18, 2027, subject to earlier conversion, redemption or repurchase.

The Notes are convertible at the option of the holder at any time until the business day prior to the maturity date, including in connection with a redemption by the Company. The Notes were initially convertible into shares of Common Stock based on a conversion rate of 28.623257 shares of Common Stock per $1,000 principal amount of the Notes (which is equal to a conversion price of $34.936625 per share, in each case subject to customary anti-dilution and other adjustments (as described in the Indenture). If the closing price per share of Common Stock on the New York Stock Exchange is at least 130% of the initial conversion price for 20 consecutive trading days, we may elect to convert the principal and accrued interest owing under the Notes, plus a make-whole amount equal to the sum of the present values of the remaining interest payments that would have otherwise been payable from the date of such conversion, redemption or repurchase, as applicable, through maturity, into Common Stock at the initial conversion price.

The 2022 Purchase Agreements required us to prepare and file a registration statement with the SEC within 75 days of the closing of each respective private placement to register the resale of the 1,791,986 shares of Common Stock, the Notes, including additional Notes issued as PIK interest through maturity, and the shares of Common Stock issuable upon conversion of Notes, including the PIK Interest accrued through maturity, and to use commercially reasonable efforts to have such registration statement declared effective within 30 days following the filing of the registration statement if there is no review by the SEC, or within 120 days following the filing of the registration statement in the event of such a review.

The 2022 Purchase Agreements contain customary representations, registration rights, warranties and agreements by us, customary conditions to closing, indemnification obligations by us, including for liabilities under the Securities Act, termination provisions, and other obligations and rights of the parties. The representations, warranties and covenants contained in the 2022 Purchase Agreements were made only for purposes of such agreements and as of specific dates, were solely for the benefit of the parties to such agreements, and may be subject to limitations agreed upon by the contracting parties.

Pursuant to the 2022 Purchase Agreements, we filed a registration statement on Form S-3 (File No. 333-264672) with the SEC on May 4, 2022 to register up to an aggregate of 6,344,585 shares of Common Stock, which consisted of (i) up to 4,552,599 shares of Common Stock issuable upon conversion of Notes, including the PIK Interest accrued through maturity (assuming all interest is paid in the form of PIK Interest), and (ii) up to 1,791,986 shares of Common Stock issued pursuant to the 2022 SPA (the “2022 Registration Statement”). The 2022 Registration Statement was declared effective on May 13, 2022.

On November 28, 2022, we entered into an amendment to the Notes with the selling shareholder (the “Notes Amendment”), whereby the initial conversion price was reduced by $5.00 from $34.936625 per share to $29.936625 per share by increasing the initial conversion rate from 28.623257 shares of Common Stock per $1,000 principal amount of the Notes to 33.400100 shares of Common Stock per $1,000 principal amount of the Notes.

The Notes, as amended by the Notes Amendment, including the PIK Interest accrued through maturity (assuming all interest is paid in the form of PIK Interest), are convertible into an aggregate of up to 5,290,092 shares of Common Stock at the conversion price of $29.936625 per share established by the Notes Amendment. The 5,290,092 shares of Common Stock issuable pursuant to the Notes and the 1,791,986 shares of Common Stock issued pursuant to the 2022 SPA are collectively referred to herein as the 2022 PIPE Shares.

2022 Underwritten Offering

On November 29, 2022, we entered into an underwriting agreement (the “Underwriting Agreement” and together with the 2021 SPA and 2022 Purchase Agreements, the “Transaction Documents”) with Cowen and

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Company, LLC and Barclays Capital Inc., as representatives of the several underwriters named in Schedule A therein (the “Underwriters”), relating to the underwritten public offering of 25,263,158 shares of Common Stock (the “2022 Offering”). The price to the public in the 2022 Offering was $9.50 per share. In addition, under the terms of the Underwriting Agreement, we granted the Underwriters an option, exercisable for 30 days, to purchase up to 3,789,473 additional shares of Common Stock to cover over-allotments, if any. In connection with the 2022 Offering, the Underwriters sold to the selling shareholder 10,526,316 shares of Common Stock at a price of $9.50 per share (the “2022 Offering Shares” and together with the 2022 PIPE Shares and the 2021 Shares, the “Shares”), resulting in an aggregate purchase price of $100.0 million.

The Underwriting Agreement contains customary representations, warranties and agreements by us, customary conditions to closing, indemnification obligations of us and the Underwriters, including for liabilities under the Securities Act, other obligations of the parties and termination provisions. The 2022 Offering was made pursuant to our effective registration statement on Form S-3ASR (File No. 333-263622) previously filed with the SEC and a related prospectus supplement and accompanying prospectus.

As of the date of this prospectus, the selling shareholder is deemed to be our affiliate. We have agreed to register for resale on the registration statement of which this prospectus is a part all the Shares held by the selling shareholder. Such registration statement supersedes the 2021 Registration Statement and the 2022 Registration Statement.

USE OF PROCEEDS

We will not receive any proceeds from the sale of the Shares by the selling shareholder.

The selling shareholder will pay all underwriting discounts, selling commissions and expenses incurred by it for brokerage, accounting, tax or legal services or the services of any other advisor to the selling shareholder incurred by the selling shareholder in connection with the sale of the Shares, if any. We will bear all other costs, fees and expenses incurred in effecting the registration of the Shares covered by this prospectus, including, without limitation, all registration and filing fees, NYSE listing fees and fees and expenses of our counsel and our accountants.

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SELLING SHAREHOLDER

The Shares being offered for resale by the selling shareholder pursuant to the Form S-3 of which this prospectus forms a part are the Shares issued to the selling shareholder or its affiliates pursuant to the Transaction Documents and held, as of the date of this prospectus, by the selling shareholder. For additional information regarding the issuance of those Shares and our relationship with the selling shareholder, see “Description of the Transactions” above. We are registering the Shares in order to permit the selling shareholder to offer the Shares for resale from time to time.

The table below lists the selling shareholder and other information regarding the beneficial ownership of shares of Common Stock by the selling shareholder. The second column lists the number of shares of Common Stock beneficially owned by the selling shareholder, assuming that all interest payments under the Notes will be paid in the form of PIK Interest. The third column lists the maximum number of shares of Common Stock that may be offered and sold by the selling shareholder pursuant to this prospectus. The fourth column lists the shares of Common Stock held by the selling shareholder after completion of this offering. The fifth column lists the percentage ownership held by the selling shareholder after completion of this offering to the extent such percentage exceeds 1% of the total number of shares of Common Stock outstanding at that time.

Pursuant to Rules 13d-3 and 13d-5 of the Exchange Act, beneficial ownership includes any shares of our Common Stock as to which a shareholder has sole or shared voting power or investment power, and also any shares of our Common Stock which the shareholder has the right to acquire within 60 days of May 1, 2024. The information presented regarding the selling shareholder is based, in part, on information the selling shareholder provided to us in writing specifically for use in this prospectus. For purposes of calculating the number of shares covered by this prospectus, we have assumed and given effect to the payment of all interest payments under the Notes through maturity in the form of PIK Interest.

The selling shareholder has not been an officer or director of the Company or of our affiliates within the past three years and except as described in this prospectus, to our knowledge, the selling shareholder has not had any material relationship with us or our affiliates within the past three years. Our knowledge is based on information provided by the selling shareholder in connection with the filing of this prospectus, as well as information obtained from relevant Schedule 13D and 13G filings.

The information below assumes the offer and sale of all of the Shares registered hereby and assumes no further acquisitions or dispositions of Common Stock by the selling shareholder. The selling shareholder may sell all, some or none of its shares in this offering. See “Plan of Distribution.”

In addition to the assumptions described above, beneficial ownership is determined in accordance with the rules of the SEC and generally includes voting or investment power over securities, except that, for purposes of calculating the number of shares covered by this prospectus, we have assumed and given effect to the payment of all interest payments under the Notes through maturity in the form of PIK Interest. To our knowledge, unless otherwise indicated, the entity named in the table below has sole voting and investment power with respect to its shares of Common Stock. Percentage of beneficial ownership is based on 76,161,210 shares of our Common Stock outstanding as of May 1, 2024.

Name of Selling Shareholder	Number of Shares of Common Stock Owned Prior to Offering		Maximum Number of Shares of Common Stock to be Sold Pursuant to this Prospectus		Number of Shares of Common Stock Owned After Offering		Percentage of Shares of Common Stock Owned After Offering (to the extent greater than 1%)
Wood River Capital, LLC(1)		21,070,518		21,070,518		—		—

(1) The number of securities shown as beneficially owned by Wood River Capital, LLC, or Wood River, prior to this offering consists of (i) 15,780,426 shares of Common Stock, and (ii) 5,290,092 shares of Common

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Stock, which is the minimum number of shares that Wood River is entitled to receive upon conversion of the Notes, as amended by the Notes Amendment, based on a reduced conversion price of $29.936625 per share, including the PIK Interest accrued through maturity (assuming all interest payments through maturity are made in the form of PIK Interest). See “Description of the Transactions” for a description of the terms of each Transaction Document. Wood River is a subsidiary of SCC Holdings LLC, or SCC Holdings, and SCC Holdings is a subsidiary of KIM, LLC, or KIM. KIM is a subsidiary of Koch Investments Group, LLC, or KIG, and KIG is a subsidiary of Koch Investments Group Holdings, LLC, or KIGH. KIGH is a subsidiary of Koch Industries, Inc., or Koch Industries. Koch Industries, SCC Holdings, KIM, KIG, and KIGH may be deemed to beneficially own the shares of Common Stock held by Wood River by virtue of their ownership of Wood River. Wood River’s principal address is 4111 E 37th St N, Wichita, Kansas 67220.

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PLAN OF DISTRIBUTION

We are registering the Shares issued pursuant to the respective Transaction Documents to permit the resale of these Shares by the selling shareholder from time to time after the date of this prospectus. We will not receive any of the proceeds from the sale by the selling shareholder of the Shares.

The selling shareholder, as used herein, includes donees, pledgees, transferees or other successors in interest selling shares of Common Stock or interests in shares of Common Stock received after the date of this prospectus from a selling shareholder as a gift, pledge, partnership distribution or other transfer.

The selling shareholder, may, from time to time, sell, transfer or otherwise dispose of any or all of its shares of Common Stock or interests in shares of Common Stock on any stock exchange, market or trading facility on which the shares are traded or in private transactions. These dispositions may be at fixed prices, at prevailing market prices at the time of sale, at varying prices determined at the time of sale, at negotiated prices, or in trading markets for the Common Stock. Such transactions may occur from time to time, together or separately.

The selling shareholder may use any one or more of the following methods when disposing of shares or interests therein:

• ordinary brokerage transactions and transactions in which the broker-dealer solicits purchasers;

• block trades in which the broker-dealer will attempt to sell the shares as agent, but may position and resell a portion of the block as principal to facilitate the transaction;

• purchases by a broker-dealer as principal and resale by the broker-dealer for its account;

• an exchange distribution in accordance with the rules of the applicable exchange;

• privately negotiated transactions;

• short sales effected after the date the registration statement of which this prospectus is a part is declared effective by the SEC;

• through the writing or settlement of options or other hedging transactions, whether through an options exchange or otherwise;

• in “at the market” offerings, as defined in Rule 415 under the Securities Act, at negotiated prices, at prices prevailing at the time of sale or prices related to such prevailing market prices, including sales made directly on a national securities exchange or sales made through a market maker other than on an exchange or other similar offerings through sales agents;

• broker-dealers may agree with the selling shareholder to sell a specified number of such shares at a stipulated price per share;

• one or more underwritten offerings on a firm commitment or best effort basis;

• any other method permitted by applicable law; and

• a combination of any such methods of sale.

The selling shareholder may, from time to time, pledge or grant a security interest in some or all of the shares of Common Stock owned by it, from time to time, under this prospectus. The selling shareholder also may transfer the shares of Common Stock in other circumstances, in which case the transferees, pledgees or other successors in interest will be the selling beneficial owners for purposes of this prospectus.

In connection with the sale of Common Stock or interests therein, the selling shareholder may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of the Common Stock in the course of hedging the positions it assumes. The selling shareholder may also sell

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shares of Common Stock short and deliver these securities to close out its short positions, or loan or pledge the Common Stock to broker-dealers that in turn may sell these securities. The selling shareholder may also enter into option or other transactions with broker-dealers or other financial institutions or the creation of one or more derivative securities which require the delivery to such broker-dealer or other financial institution of shares offered by this prospectus, which shares such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

Broker-dealers engaged by the selling shareholder may arrange for other broker-dealers to participate in sales. If the selling shareholder effects certain transactions by selling shares of Common Stock to or through underwriters, broker-dealers or agents, such underwriters, broker-dealers or agents may receive commissions in the form of discounts, concessions or commissions from such selling shareholder or commissions from purchasers of the Common Stock for whom they may act as agent or to whom they may sell as principal. Such commissions will be in amounts to be negotiated, but, except as set forth in a supplement to this prospectus, in the case of an agency transaction will not be in excess of a customary brokerage commission in compliance with applicable rules of the Financial Industry Regulatory Authority (“FINRA”); and in the case of a principal transaction, a markup or markdown in compliance with applicable FINRA rules.

To facilitate the offering of shares of Common Stock covered by this prospectus, certain persons participating in the offering may engage in transactions that stabilize, maintain or otherwise affect the price of our Common Stock. This may include over-allotments or short sales of our Common Stock, which involve the sale by persons participating in the offering of more Common Stock than the selling shareholder sold to them. In these circumstances, these persons would cover such over-allotments or short positions by making purchases in the open market or by exercising their option, if any, to purchase additional shares from the selling shareholder. The effect of these transactions may be to stabilize or maintain the market price of our Common Stock at a level above that which might otherwise prevail in the open market. These transactions may be discontinued at any time.

The aggregate proceeds to the selling shareholder from the sale of the Common Stock offered by it will be the purchase price of the Common Stock less discounts or commissions, if any. The selling shareholder reserves the right to accept and, together with its agent from time to time, to reject, in whole or in part, any proposed purchase of Common Stock to be made directly or through agents. We will not receive any of the proceeds from this offering.

The selling shareholder also may resell all or a portion of the shares in open market transactions in reliance upon Rule 144 under the Securities Act, if available, or pursuant to other available exemptions from the registration requirements under the Securities Act, rather than this prospectus, provided that it meets the criteria and conforms to the requirements of that rule. Registration of the Shares covered by this prospectus does not mean that any shares of the Common Stock will be offered or sold.

The selling shareholder may engage in at-the-market offerings and offer the Common Stock into an existing trading market in accordance with Rule 415(a)(4) under the Securities Act on the terms described in a prospectus supplement relating thereto. Underwriters, dealers and agents who participate in any at-the-market-offerings will be described in such prospectus supplement relating thereto.

In connection with a distribution of securities pursuant to this prospectus, the selling shareholder and any underwriters, broker-dealers or agents that participate in the sale of the Common Stock or interests therein may be deemed to be “underwriters” within the meaning of Section 2(11) of the Securities Act, and any discounts, commissions, concessions or profit earned by broker-dealers on any resale of the shares may be considered underwriting discounts and commissions under the Securities Act. Any “underwriter” within the meaning of Section 2(11) of the Securities Act, in connection with the sale of Shares under this prospectus, will be subject to the prospectus delivery requirements of the Securities Act. To the extent applicable we will make copies of this prospectus (as it may be supplemented or amended from time to time) available for the purpose of satisfying the prospectus delivery requirements of the Securities Act.

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To the extent required, the shares of our Common Stock to be sold, the name of the selling shareholder, the respective purchase prices and public offering prices, the names of any agents, dealer or underwriter, and any applicable commissions or discounts with respect to a particular offer will be set forth in an accompanying prospectus supplement or, if appropriate, a post-effective amendment to the registration statement that includes this prospectus.

In order to comply with the securities laws of some states, if applicable, the Common Stock may be sold in these jurisdictions only through registered or licensed brokers or dealers. In addition, in some states the Common Stock may not be sold unless it has been registered or qualified for sale or an exemption from registration or qualification requirements is available and is complied with.

If at the time of any offering made under this prospectus, a member of FINRA participating in the offering has a “conflict of interest” as defined in FINRA Rule 5121 (“Rule 5121”), that offering will be conducted in accordance with the relevant provisions of Rule 5121.

We have advised the selling shareholder that the anti-manipulation rules of Regulation M promulgated under the Exchange Act may apply to certain sales of shares in the market and to the activities of the selling shareholder and its affiliates.

The selling shareholder may indemnify broker-dealers that participate in transactions involving the sale of the shares against certain liabilities, including liabilities arising under the Securities Act.

We have agreed to indemnify the selling shareholder against liabilities, including liabilities under the Securities Act and state securities laws, relating to the registration of the Shares offered by this prospectus.

We have agreed with the selling shareholder to use our commercially reasonable efforts to keep the registration statement of which this prospectus constitutes a part effective until the date on which all of the shares included in the registration statement have actually been sold.

We will pay all expenses of the registration of the Shares pursuant to the respective Transaction Documents, including, without limitation, SEC filing fees and expenses of compliance with state securities or “blue sky” laws; provided, however, that a selling shareholder will pay all underwriting discounts and selling commissions, if any.

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LEGAL MATTERS

The validity of the Shares registered hereunder has been passed upon for us by Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., Boston, Massachusetts.

EXPERTS

The consolidated financial statements of Aspen Aerogels, Inc. as of December 31, 2023 and 2022, and for each of the years in the three-year period ended December 31, 2023, and management’s assessment of the effectiveness of internal control over financial reporting as of December 31, 2023 have been incorporated by reference herein and in the registration statement in reliance upon the report of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

As permitted by SEC rules, this prospectus, which constitutes a part of a registration statement on Form S-3 that we have filed with the SEC, omits certain of the information set forth in the registration statement. Accordingly, you should refer to the registration statement and its exhibits for further information with respect to us and our Common Stock. Copies of the registration statement and its exhibits are on file at the offices of the SEC. This prospectus contains statements concerning documents filed as exhibits. For the complete text of any of these documents, we refer you to the copy of the document filed as an exhibit to the registration statement.

We file annual, quarterly and current reports, proxy and information statements and other information with the SEC. The SEC also maintains an Internet site that contains reports, proxy and information statements, and other information regarding issuers that file electronically with the SEC. The address of that site is www.sec.gov.

We also maintain a website at http://www.aerogel.com with information about our company and through which you may access these materials and other filings with the SEC free of charge as soon as reasonably practicable after they are filed electronically with, or furnished to, the SEC. Except for the documents incorporated by reference as described below under “Incorporation of Certain Documents by Reference”, information contained on our website or any other website is not incorporated into this prospectus and does not constitute a part of this prospectus. Our website address referenced above is intended to be an inactive textual reference only and not an active hyperlink to our website.

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INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows us to “incorporate by reference” into this prospectus the information we file with the SEC, which means that we can disclose important information to you by referring you to other documents filed separately with the SEC. The information incorporated by reference is considered part of this prospectus, and any information that we file with the SEC subsequent to this prospectus and prior to the termination of the offering referred to in this prospectus will automatically be deemed to update and supersede this information. We incorporate by reference into this prospectus the documents listed below (excluding any portions of such documents that have been “furnished” but not “filed” for purposes of the Exchange Act unless specifically incorporated by reference herein or therein):

• Our Annual Report on Form 10-K for the year ended December 31, 2023, filed with the SEC on March 7, 2024;

• Our Quarterly Report on Form 10-Q for the quarter ended March 31, 2024 filed with the SEC on May 2, 2024;

• The portions of our Definitive Proxy Statement on Schedule 14A filed with the SEC on April 10, 2024 that are deemed “filed” with the SEC under the Exchange Act;

• Our Current Report on Form 8-K filed March 7, 2024; and

• The description of our common stock contained in our registration statement on Form 8-A12B filed June 6, 2014, including any other amendments or reports filed for the purpose of updating such description (other than any portion of such filings that are furnished under applicable SEC rules rather than filed).

We also incorporate by reference all documents we subsequently file with the SEC (other than information furnished pursuant to Item 2.02 or Item 7.01 of Form 8-K or as otherwise permitted by SEC rules) pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the initial filing of the registration statement of which this prospectus is a part (including prior to the effectiveness of the registration statement) and prior to the termination of the offering.

This prospectus is part of a registration statement on Form S-3 that we have filed with the SEC relating to the securities. As permitted by SEC rules, this prospectus does not contain all of the information included in the registration statement and the accompanying exhibits and schedules we file with the SEC. We have filed certain legal documents that control the terms of the Common Stock offered by this prospectus as exhibits to the registration statement. We may file certain other legal documents that control the terms of the Common Stock offered by this prospectus as exhibits to reports we file with the SEC. You may refer to the registration statement and the exhibits and schedules for more information about us and our securities. The registration statement and exhibits and schedules are also available through the SEC’s website at www.sec.gov.

We will provide, without charge and upon oral or written request, to each person, including any beneficial owner, to whom a copy of this prospectus has been delivered, a copy of any of the documents referred to above as being incorporated by reference into this prospectus but not delivered with it. You may obtain a copy of these filings, at no cost, by writing or calling us at Aspen Aerogels, Inc., Attn: Investor Relations, 30 Forbes Road, Building B, Northborough, MA 01532, (508) 691-1111. Exhibits to the filings will not be provided, however, unless those exhibits have been specifically incorporated by reference in this prospectus.

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21,070,518 Shares

Common Stock

PROSPECTUS

PART II. INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution

The following expenses incurred in connection with the sale of the securities being registered will be borne by the registrant. Other than the SEC registration fee, the amounts stated are estimates.

SEC Registration Fee	$	26,692
Legal Fees and Expenses	$	50,000
Accounting Fees and Expenses	$	30,000
Miscellaneous	$	5,000
Total	$	111,692

Item 15. Indemnification of Directors and Officers

Delaware General Corporation Law. Subsection (a) of Section 145 of the Delaware General Corporation Law (the “DGCL”) provides that a corporation may indemnify any person who was or is a party or is threatened to be made a party to any threatened, pending or completed action, suit or proceeding, whether civil, criminal, administrative or investigative (other than an action by or in the right of the corporation) by reason of the fact that he or she is or was a director, officer, employee or agent of the corporation, or is or was serving at the request of the corporation as a director, officer, employee or agent of another corporation, partnership, joint venture, trust or other enterprise, against expenses (including attorneys’ fees), judgments, fines and amounts paid in settlement actually and reasonably incurred by the person in connection with such action, suit or proceeding if he or she acted in good faith and in a manner he or she reasonably believed to be in or not opposed to the best interests of the corporation, and, with respect to any criminal action or proceeding, had no reasonable cause to believe his or her conduct was unlawful. Section 145 of the DGCL further provides that a corporation similarly may indemnify any such person serving in any such capacity who was or is a party or is threatened to be made a party to any threatened, pending or completed action or suit by or in the right of the corporation to procure a judgment in its favor, against expenses (including attorneys’ fees) actually and reasonably incurred in connection with the defense or settlement of such action or suit if he or she acted in good faith and in a manner he or she reasonably believed to be in or not opposed to the best interests of the corporation and except that no indemnification shall be made in respect of any claim, issue or matter as to which such person shall have been adjudged to be liable to the corporation unless and only to the extent that the Delaware Court of Chancery or such other court in which such action or suit was brought shall determine upon application that, despite the adjudication of liability but in view of all of the circumstances of the case, such person is fairly and reasonably entitled to indemnity for such expenses which the Court of Chancery or such other court shall deem proper.

Restated Certificate of Incorporation and Amended and Restated Bylaws. Our restated certificate of incorporation limits the liability of our directors and officers to the fullest extent permitted by Delaware law. Our restated certificate of incorporation and amended and restated bylaws also provide that we will indemnify and advance expenses to any of our directors and officers who, by reason of the fact that he or she is one of our officers or directors, is involved in a legal proceeding of any nature. We will repay certain expenses incurred by a director or officer in connection with any civil, criminal, administrative or investigative action or proceeding, including actions by us or in our name. Such indemnifiable expenses include, to the maximum extent permitted by law, attorney’s fees, judgments, fines, ERISA excise taxes, penalties, settlement amounts and other expenses reasonably incurred in connection with legal proceedings. A director or officer will not receive indemnification if he or she is found not to have acted in good faith and in a manner he or she reasonably believed to be in, or not opposed to, our best interest.

Indemnification Agreements. We have entered into indemnification agreements with each of our non-employee directors and with certain officers. These agreements provide that we will, among other things, indemnify and advance expenses to our directors and officers for certain expenses, including attorneys’ fees,

PART II - 1

judgments, fines and settlement amounts incurred by any such person in any investigation, action or proceeding, including any action by us arising out of such person’s services as our director or officer, or any other company or enterprise to which the person provides services at our request. We believe that these provisions and agreements are necessary to attract and retain qualified persons as directors and officers.

Insurance Policies. We have obtained director and officer liability insurance to cover liabilities our directors and officers may incur in connection with their services to us.

The foregoing discussion of our restated certificate of incorporation, amended and restated bylaws, indemnification agreements, indemnity agreement, and Delaware law is not intended to be exhaustive and is qualified in its entirety by such restated certificate of incorporation, amended and restated bylaws, indemnification agreements, indemnity agreement, or law.

Item 16. Exhibits

The exhibits to this registration statement are listed in the Exhibit Index to this registration statement, which immediately precedes the Signature Page and which Exhibit Index is hereby incorporated by reference.

Item 17. Undertakings

(a) The undersigned registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) To include any prospectus required by section 10(a)(3) of the Securities Act of 1933;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20% change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective registration statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement; provided, however, that paragraphs (a)(1)(i), (a)(1)(ii) and (a)(1)(iii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Commission by the registrant pursuant to section 13 or section 15(d) of the Securities Exchange Act of 1934 that are incorporated by reference in the registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the registration statement.

(2) That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

PART II - 2

(4) That, for the purpose of determining liability under the Securities Act of 1933 to any purchaser:

(i) Each prospectus filed by the registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

(ii) Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5), or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(1)(i), (vii), or (x) for the purpose of providing the information required by section 10(a) of the Securities Act of 1933 shall be deemed to be part of and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which that prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof. Provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such effective date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date.

(5) That, for the purpose of determining liability of the registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities, in a primary offering of securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

(i) Any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

(ii) Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

(iii) The portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

(iv) Any other communication that is an offer in the offering made by the undersigned registrant to the purchaser.

(b) That, for purposes of determining any liability under the Securities Act:

(1) The information omitted from the form of prospectus filed as part of the registration statement in reliance upon Rule 430A and contained in the form of prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4) or 497(h) under the Securities Act shall be deemed to be part of the registration statement as of the time it was declared effective; and

(2) Each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(c) The undersigned registrant hereby undertakes that, for purposes of determining any liability under the Securities Act of 1933, each filing of the registrant’s annual report pursuant to section 13(a) or section 15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan’s

PART II - 3

annual report pursuant to section 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(d) Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant, the registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

(e) The undersigned registrant hereby undertakes to file an application for the purpose of determining the eligibility of the trustee to act under subsection (a) of Section 310 of the Trust Indenture Act (“Act”) in accordance with the rules and regulations prescribed by the Commission under section 305(b)(2) of the Act.

PART II - 4

EXHIBIT INDEX

Exhibit Number	Exhibit Description	Filed with this Report		Incorporated by Reference herein from Form or Schedule		Filing Date		SEC File/Reg. Number
3.1	Restated Certificate of Incorporation of the Registrant, as filed with the Secretary of State of the State of Delaware on June  18, 2014.				Form 8-K (Exhibit 3.2)		06/19/14		001-36481
3.1.2	Certificate of Amendment to Restated Certificate of Incorporation of Aspen Aerogels, Inc., dated June 1, 2023.				Form 8-K (Exhibit 3.1)		06/1/23		001-36481
3.2	Amended and Restated Bylaws of Aspen Aerogels, Inc.				Form 10-K (Exhibit 3.2)		03/07/24		001-36481
4.1	Form of common stock certificate.				Amendment No. 1 to Form S-1 (Exhibit 4.1)		05/14/14		333-195523
4.2	Description of Securities.				Form 10-K (Exhibit 4.3)		03/06/20		001-36481
4.3	Form of Note (including Indenture incorporated by reference therein).				Form 8-K (Exhibit 4.1)		02/17/22		001-36481
10.1	Note Purchase Agreement, dated February 15, 2022, by and between the Registrant and Wood River Capital, LLC.				Form 8-K (Exhibit 10.1)		02/17/22		001-36481
10.1.1	Amendment to Note Purchase Agreement, dated November 28, 2022, by and between the Registrant and Wood River Capital, LLC.				Form 8-K (Exhibit 10.2)		11/29/22		001-36481
10.2	Securities Purchase Agreement, dated February 15, 2022, by and between the Registrant and Wood River Capital, LLC.				Form 8-K (Exhibit 10.2)		02/17/22		001-36481
10.3	Amendment No. 1 to Convertible Senior PIK Toggle Notes due 2027, dated November 28, 2022.				Form 8-K (Exhibit 10.3)		11/29/22		001-36481
10.4	Securities Purchase Agreement dated June 29, 2021, by and between the Registrant and Spring Creek Capital, LLC.				Form 8-K (Exhibit 10.1)		06/30/21		001-36481
5.1	Opinion of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C. with respect to the legality of the securities being registered.		X
23.1	Consent of KPMG LLP.		X
23.2	Consent of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C. (included in Exhibit 5.1).		X
24.1	Powers of Attorney (included on signature page to this registration statement).		X
107	Calculation of Filing Fee Table.		X

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the city of Northborough, Massachusetts, on May 2, 2024.

ASPEN AEROGELS, INC.
By:	/s/ Donald R. Young
	Donald R. Young
	President and Chief Executive Officer

POWER OF ATTORNEY

We, the undersigned officers and directors of Aspen Aerogels, Inc., hereby severally constitute and appoint Donald R. Young, and Ricardo C. Rodriguez, and each of them singly (with full power to each of them to act alone), our true and lawful attorneys-in-fact and agents, with full power of substitution and resubstitution in each of them or him and in his name, place and stead, and in any and all capacities, to sign any and all amendments (including post-effective amendments) to this registration statement (or any other registration statement for the same offering that is to be effective upon filing pursuant to Rule 462(b) under the Securities Act of 1933), and to file the same, with all exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as full to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them or their or his substitute or substitutes may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed below by the following persons in the capacities and on the dates indicated.

Signature	Title	Date
/s/ Donald R. Young Donald R. Young	President, Chief Executive Officer and Director (principal executive officer)	May 2, 2024
/s/ Ricardo C. Rodriguez Ricardo C. Rodriguez	Chief Financial Officer and Treasurer (principal financial officer)	May 2, 2024
/s/ Santhosh P. Daniel Santhosh P. Daniel	Chief Accounting Officer (principal accounting officer)	May 2, 2024
/s/ William P. Noglows William P. Noglows	Chairperson of the Board	May 2, 2024
/s/ Rebecca B. Blalock Rebecca B. Blalock	Director	May 2, 2024
/s/ James E. Sweetnam James E. Sweetnam	Director	May 2, 2024
/s/ Kathleen M. Kool Kathleen M. Kool	Director	May 2, 2024
/s/ Steven R. Mitchell Steven R. Mitchell	Director	May 2, 2024
/s/ Mark L. Noetzel Mark L. Noetzel	Director	May 2, 2024