ASPEN AEROGELS INC

On February 26, 2024, Donald R. Young, our President, Chief Executive Officer, and member of our board of directors, adopted a trading plan intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) under the Exchange Act. The plan provides for the sale of up to 691,124 shares at specific market prices, subject to specified limitations, during pre-determined sale periods. The plan was established for the purposes of facilitating the exercise and subsequent sale of stock options with a ten-year contractual life that are due to expire between September 2024 and December 2025 (the “Options”), by facilitating the sale of shares solely to raise sufficient proceeds to cover the exercise cost and taxes associated with the exercise of the Options. The plan expires on the earlier of (i) the date all of the shares under the plan have been sold and (ii)December 11, 2025.

Except as disclosed above, none of our directors or executive officers adopted, modified orterminated any contract, instruction or written plan for the purchase or sale of our securities that was intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) or any “non-Rule 10b5-1 trading arrangement” as such term is defined in Item 408(a) of Regulation S-K, during the fiscal quarter ended March 31, 2024.