X0508 4 2023-09-05 0 0001145986 ASPEN AEROGELS INC ASPN 0001610279 Mitchell Steven R C/O ASPEN AEROGELS, INC. 30 FORBES ROAD, BUILDING B NORTHBOROUGH MA 01532 1 0 0 0 0 Common Stock 2023-09-05 4 P 0 50000 6.1691 A 126719 D The price reported represents a weighted average price. These shares were purchased in multiple transactions at prices ranging from $6.115 to $6.19 per share. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price. Includes 7,488 shares of Restricted Stock. /s/ Virginia H. Johnson, Attorney-in-Fact 2023-09-06