Exhibit 4.1 AVANTOR, INC. DESCRIPTION OF CAPITAL STOCK The following is a description of the material terms of our capital stock, and is qualified in its entirety by, our third amended and restated certificate of incorporation and third amended and restated bylaws, each of which is incorporated by reference as an exhibit to the Annual Report on Form 10-K of which this Exhibit 4.1 is a part. Our common stock is our only security registered pursuant to Section 12 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). Our purpose is to engage in any lawful act or activity for which corporations may now or hereafter be organized under the Corporation Law of the State of Delaware (as the same exists or may hereafter be amended from time to time, the “DGCL”). Our authorized capital stock consists of 750,000,000 shares of common stock, par value $0.01 per share, and 75,000,000 shares of preferred stock, par value $0.01 per share. Unless our Board of Directors determines otherwise, we will issue all shares of our capital stock in uncertificated form. Common stock Holders of our common stock are entitled to one vote for each share held of record on all matters on which stockholders are entitled to vote generally, including the election or removal of directors, subject to certain limitations. The holders of our common stock do not have cumulative voting rights in the election of directors. Upon our liquidation, dissolution or winding up or the sale of all or substantially all of our assets and after payment in full of all amounts required to be paid to creditors and to the holders of preferred stock having liquidation preferences, if any, the holders of our common stock will be entitled to receive our remaining assets available for distribution on a pro rata basis. Holders of our common stock do not have preemptive, subscription, redemption or conversion rights. The common stock is not subject to further calls or assessment by us. There are no redemption or sinking fund provisions applicable to the common stock. All shares of our common stock that are outstanding are fully paid and non- assessable. The rights, powers, preferences and privileges of holders of our common stock will be subject to those of the holders of any shares of our preferred stock we may authorize and issue in the future. Preferred stock Our third amended and restated certificate of incorporation authorizes our Board of Directors to establish one or more series of preferred stock (including convertible preferred stock). Unless required by law or by the rules of the NYSE, the authorized shares of preferred stock will be available for issuance without further stockholder action. Our Board of Directors is able to determine, with respect to any series of preferred stock, the terms and rights of that series, including:

• the designation of the series; • the number of shares of the series, which our Board of Directors may, except where otherwise provided in the preferred stock designation, increase (but not above the total number of authorized shares of the class) or decrease (but not below the number of shares then outstanding); • whether dividends, if any, will be cumulative or non-cumulative and the dividend rate of the series; • the dates at which dividends, if any, will be payable; • the redemption rights and price or prices, if any, for shares of the series; • the terms and amounts of any sinking fund provided for the purchase or redemption of shares of the series; • the amounts payable on shares of the series in the event of any voluntary or involuntary liquidation, dissolution or winding-up of the affairs of our company; • whether the shares of the series will be convertible into shares of any other class or series, or any other security, of our company or any other corporation, and, if so, the specification of the other class or series or other security, the conversion price or prices or rate or rates, any rate adjustments, the date or dates as of which the shares will be convertible and all other terms and conditions upon which the conversion may be made; • restrictions on the issuance of shares of the same series or of any other class or series; and • the voting rights, if any, of the holders of the series. We could issue a series of preferred stock that could, depending on the terms of the series, impede or discourage an acquisition attempt or other transaction that some, or a majority, of you might believe to be in your best interests or in which you might receive a premium for your common stock over the market price of the common stock. Additionally, the issuance of preferred stock may adversely affect the holders of our common stock by restricting dividends on the common stock, diluting the voting power of the common stock or subordinating the liquidation rights of the common stock. As a result of these or other factors, the issuance of preferred stock could have an adverse impact on the market price of our common stock. Dividends The DGCL permits a corporation to declare and pay dividends out of “surplus” or, if there is no “surplus,” out of its net profits for the fiscal year in which the dividend is declared and/or the preceding year. “Surplus” is defined as the excess of the net assets of the corporation over the amount determined to be the capital of the corporation by the Board of Directors. The capital of the corporation is typically calculated to be (and cannot be less than) the aggregate par value of

all issued shares of capital stock. Net assets equal the fair value of the total assets minus total liabilities. The DGCL also provides that dividends may not be paid out of net profits if, after the payment of the dividend, capital is less than the capital represented by the outstanding stock of all classes having a preference upon the distribution of assets. Declaration and payment of any dividend will be subject to the discretion of our Board of Directors. The time and amount of dividends will be dependent upon our financial condition, operations, cash requirements and availability, debt repayment obligations, capital expenditure needs and restrictions in our debt instruments, industry trends, the provisions of Delaware law affecting the payment of dividends to stockholders and any other factors our Board of Directors may consider relevant. Anti-takeover effects of our third amended and restated Certificate of Incorporation and third amended and restated bylaws and certain provisions of Delaware Law Our third amended and restated certificate of incorporation, third amended and restated bylaws and the DGCL, which are summarized in the following paragraphs, contain provisions that are intended to enhance the likelihood of continuity and stability in the composition of our Board of Directors. These provisions are intended to avoid costly takeover battles, reduce our vulnerability to a hostile change of control and enhance the ability of our Board of Directors to maximize stockholder value in connection with any unsolicited offer to acquire us. However, these provisions may have an anti-takeover effect and may delay, deter or prevent a merger or acquisition of our company by means of a tender offer, a proxy contest or other takeover attempt that a stockholder might consider is in its best interest, including those attempts that might result in a premium over the prevailing market price for the shares of common stock held by stockholders. Authorized but unissued capital stock Delaware law does not require stockholder approval for any issuance of authorized shares. However, the listing requirements of the NYSE, which would apply if and so long as our common stock remains listed on the NYSE, require stockholder approval of certain issuances equal to or exceeding 20% of the then outstanding voting power or then outstanding number of shares of common stock. These additional shares may be used for a variety of corporate purposes, including future public offerings, to raise additional capital or to facilitate acquisitions. Our Board of Directors may issue shares of preferred stock on terms calculated to discourage, delay or prevent a change of control of our company or the removal of our management. Moreover, our authorized but unissued shares of preferred stock will be available for future issuances without stockholder approval and could be utilized for a variety of corporate purposes, including future offerings to raise additional capital, acquisitions and employee benefit plans. One of the effects of the existence of unissued and unreserved common stock or preferred stock may be to enable our Board of Directors to issue shares to persons friendly to current management, which issuance could render more difficult or discourage an attempt to obtain

control of our company by means of a merger, tender offer, proxy contest or otherwise, and thereby protect the continuity of our management and possibly deprive our stockholders of opportunities to sell their shares of common stock at prices higher than prevailing market prices. Business combinations We have opted out of Section 203 of the DGCL; however, our third amended and restated certificate of incorporation contains similar provisions providing that we may not engage in certain “business combinations” with any “interested stockholder” for a three-year period following the time that the stockholder became an interested stockholder, unless: • prior to such time, our Board of Directors approved either the business combination or the transaction which resulted in the stockholder becoming an interested stockholder; • upon consummation of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of our voting stock outstanding at the time the transaction commenced, excluding certain shares; or • at or subsequent to that time, the business combination is approved by our Board of Directors and by the affirmative vote of holders of at least 662/3% of the outstanding voting stock that is not owned by the interested stockholder. However, such restrictions will not apply if a stockholder becomes an interested stockholder inadvertently and (i) as soon as practicable divests itself of ownership of sufficient shares so that the stockholder ceases to be an interested stockholder and (ii) would not, at any time within the three-year period immediately prior to a business combination between the Company and such stockholder, have been an interested stockholder but for the inadvertent acquisition of ownership. Generally, a “business combination” includes a merger, asset or stock sale or other transaction resulting in a financial benefit to the interested stockholder. Subject to certain exceptions, an “interested stockholder” is a person who, together with that person’s affiliates and associates, owns, or within the previous three years owned, 15% or more of our voting stock. For purposes of this section only, “voting stock” has the meaning given to it in Section 203 of the DGCL. Under certain circumstances, this provision will make it more difficult for a person who would be an “interested stockholder” to effect various business combinations with a corporation for a three-year period. This provision may encourage companies interested in acquiring our company to negotiate in advance with our Board of Directors because the stockholder approval requirement would be avoided if our Board of Directors approves either the business combination or the transaction which results in the stockholder becoming an interested stockholder. These provisions also may have the effect of preventing changes in our Board of Directors and may make it more difficult to accomplish transactions which stockholders may otherwise deem to be in their best interests.

Our third amended and restated certificate of incorporation provides that New Mountain Capital and its affiliates and any of its direct or indirect transferees and any group as to which such persons are a party do not constitute “interested stockholders” for purposes of this provision. Removal of Directors; Vacancies Our third amended and restated certificate of incorporation and third amended and restated bylaws provide that directors may be removed either with or without cause upon the affirmative vote of a majority of the voting power of all outstanding shares of stock entitled to vote generally in the election of directors, voting together as a single class. In addition, our third amended and restated certificate of incorporation and our third amended and restated bylaws also provide that, subject to the rights granted to one or more series of preferred stock then outstanding, any vacancies on our Board of Directors will be filled only by the affirmative vote of a majority of the remaining directors, even if less than a quorum, or by a sole remaining director. No cumulative voting Under Delaware law, the right to vote cumulatively does not exist unless the certificate of incorporation specifically authorizes cumulative voting. Our third amended and restated certificate of incorporation does not authorize cumulative voting. Therefore, stockholders holding a majority in voting power of the shares of our stock entitled to vote generally in the election of directors are able to elect all our directors. Special stockholder meetings Our third amended and restated certificate of incorporation provides that special meetings of our stockholders may be called at any time only by or at the direction of the Board of Directors or the chairman of the Board of Directors; however, stockholders of record who own shares of common stock representing at least 20% of the relevant voting power continuously for at least one year can request that the Board of Directors call a special meeting of stockholders, provided that the stockholders satisfy specified requirements. Proxy Access Our third amended and restated bylaws provide for proxy access, which permits a stockholder, or a group of up to 20 stockholders, owning 3% or more of our outstanding common stock continuously for at least three years, to nominate and include in our proxy materials qualifying director nominees constituting up to the greater of (i) two directors or (ii) twenty percent of our Board of Directors. To be timely, the notice of proxy access nomination must be addressed to and received by the Secretary not less than 120 days nor more than 150 days prior to the first anniversary of the date on which our definitive proxy statement was released to stockholders in connection with the prior year’s annual meeting; provided, however, that if the annual meeting is convened more than 30 days prior to or delayed by more than 60 days after the first anniversary of the date of the preceding year’s annual meeting, the information must be so received not earlier than 120 days prior to such annual meeting and not later than the close of business on the

later of (x) the 90th day prior to such annual meeting or (y) the 10th day following the day on which a public announcement of the date of our annual meeting is first made; provided further that in no event shall any adjournment or postponement of an annual meeting, or the public announcement thereof, commence a new time period or extend any time period for the receipt of the information. The complete proxy access provisions for director nominations are set forth in our third amended and restated bylaws. Requirements for advance notification of director nominations and stockholder proposals Our third amended and restated bylaws establish advance notice procedures with respect to stockholder proposals and the nomination of candidates for election as directors, other than nominations made by or at the direction of the Board of Directors or a committee of the Board of Directors. In order for any matter to be “properly brought” before a meeting, a stockholder will have to comply with advance notice requirements and provide us with certain information. Generally, to be timely, a stockholder’s notice must be received at our principal executive offices not less than 90 days nor more than 120 days prior to the first anniversary date of the immediately preceding annual meeting of stockholders. Our third amended and restated bylaws will also specify requirements as to the form and content of a stockholder’s notice. Our third amended and restated bylaws allow the chairman of the meeting at a meeting of the stockholders to adopt rules and regulations for the conduct of meetings which may have the effect of precluding the conduct of certain business at a meeting if the rules and regulations are not followed. These provisions may defer, delay or discourage a potential acquirer from conducting a solicitation of proxies to elect the acquirer’s own slate of directors or otherwise attempting to influence or obtain control of our company. Stockholder action by written consent Pursuant to Section 228 of the DGCL, any action required to be taken at any annual or special meeting of the stockholders may be taken without a meeting, without prior notice and without a vote if a consent or consents in writing, setting forth the action so taken, is signed by the holders of outstanding stock having not less than the minimum number of votes that would be necessary to authorize or take such action at a meeting at which all shares of our stock entitled to vote thereon were present and voted, unless our third amended and restated certificate of incorporation provides otherwise. Dissenters’ rights of appraisal and payment Under the DGCL, with certain exceptions, our stockholders will have appraisal rights in connection with a merger or consolidation of us. Pursuant to the DGCL, stockholders who properly request and perfect appraisal rights in connection with such merger or consolidation will have the right to receive payment of the fair value of their shares as determined by the Delaware Court of Chancery.

Stockholders’ derivative actions Under the DGCL, any of our stockholders may bring an action in our name to procure a judgment in our favor, also known as a derivative action, provided that the stockholder bringing the action is a holder of our shares at the time of the transaction to which the action relates or such stockholder’s stock thereafter devolved by operation of law. Exclusive forum Our third amended and restated certificate of incorporation provides that unless we consent to the selection of an alternative forum, the state or federal courts (as appropriate) located within the State of Delaware shall, to the fullest extent permitted by law, be the sole and exclusive forum for any (i) derivative action or proceeding brought on behalf of our company, (ii) action asserting a claim of breach of a fiduciary duty owed by any director, officer, or other employee or stockholder of our company to us or our stockholders, creditors or other constituents, (iii) action against us or any of our directors or officers involving a claim or defense arising pursuant to any provision of the DGCL or our third amended and restated certificate of incorporation or our third amended and restated bylaws, (iv) action against us or any director or officer of the Company involving a claim or defense implicating the internal affairs doctrine, or (v) action against us or any of our directors or officers involving a claim or defense arising pursuant to the Exchange Act or the Securities Act of 1933, as amended. It is possible that these exclusive forum provisions may be challenged in court and may be deemed unenforceable in whole or in part. Our exclusive forum provision shall not relieve the company of its duties to comply with the federal securities laws and the rules and regulations thereunder, and our stockholders will not be deemed to have waived our compliance with these laws, rules and regulations. Conflicts of interest Delaware law permits corporations to adopt provisions renouncing any interest or expectancy in certain opportunities that are presented to the corporation or its officers, directors or stockholders. Limitations on liability and indemnification of officers and directors The DGCL authorizes corporations to limit or eliminate the personal liability of directors to corporations and their stockholders for monetary damages for breaches of directors’ fiduciary duties, subject to certain exceptions. Our third amended and restated certificate of incorporation includes a provision that eliminates the personal liability of directors for monetary damages for any breach of fiduciary duty as a director, except to the extent such exemption from liability or limitation thereof is not permitted under the DGCL. The effect of these provisions is to eliminate the rights of us and our stockholders, through stockholders’ derivative suits on our behalf, to recover monetary damages from a director for breach of fiduciary duty as a director, including breaches resulting from grossly negligent behavior. However, exculpation does not apply to any director if the director has acted in bad faith, knowingly or intentionally violated the law,

authorized illegal dividends or redemptions or derived an improper benefit from his or her actions as a director. Our third amended and restated bylaws provide that we must generally indemnify, and advance expenses to, our directors and officers to the fullest extent authorized by the DGCL. We also are expressly authorized to carry directors’ and officers’ liability insurance providing indemnification for our directors, officers and certain employees for some liabilities. We also have entered into indemnification agreements with our directors, which agreements require us to indemnify these individuals to the fullest extent permitted under Delaware law against liabilities that may arise by reason of their service to us, and to advance expenses incurred as a result of any proceeding against them as to which they could be indemnified. We believe that these indemnification and advancement provisions and insurance are useful to attract and retain qualified directors and executive officers. The limitation of liability, indemnification and advancement provisions in our third amended and restated certificate of incorporation and third amended and restated bylaws may discourage stockholders from bringing a lawsuit against directors for breach of their fiduciary duty. These provisions also may have the effect of reducing the likelihood of derivative litigation against directors and officers, even though such an action, if successful, might otherwise benefit us and our stockholders. In addition, your investment may be adversely affected to the extent we pay the costs of settlement and damage awards against directors and officers pursuant to these indemnification provisions. Transfer agent and registrar The transfer agent and registrar for our common stock is American Stock Transfer & Trust Company, LLC. Listing Our common stock is listed on the NYSE under the symbol “AVTR.”