X0508 4 2025-11-13 0001145986 ASPEN AEROGELS INC ASPN 0001610257 Young Donald R C/O ASPEN AEROGELS, INC., 30 FORBES ROAD, BLDG B NORTHBOROUGH MA 01532 true true false false President and CEO true Common Stock 2025-11-13 4 S false 56845 3.23 D 494011 D The transaction reported on this Form 4 was effected pursuant to a rule 10b5-1 trading plan. This plan was previously adopted by the reporting person on August 11, 2025, to sell a limited number of shares for tax purposes in connection with a one-time personal real estate transaction. These transactions were executed in multiple trades at prices ranging from $3.15 to $3.41. The reporting person will provide to the staff of the Securities and Exchange Commission, the issuer, or any security holder of the issuer, upon request, full information regarding the number of shares sold at each separate price. Represents 414,306 shares of Common Stock and 79,705 Restricted Stock Units. Exhibit 24.1 - Power of Attorney /s/ Glenn Deegan, Attorney-in-Fact 2025-11-14