ASPEN AEROGELS INC

(a)Departure of Executive Officers and CFO Transition

On August 4, 2025, we and Ricardo C. Rodriguez, our Chief Financial Officer and Treasurer, determined that Mr. Rodriguez will depart the Company, effective as of October 1, 2025, to pursue other opportunities outside of the Company. Mr. Rodriguez’s departure is not related to any disagreement with the Company on any matter relating to the Company’s operations, policies or practices. We would like to thank Mr. Rodriguez for his contributions to the Company during a critical period of growth.

Effective October 1, 2025, we are promoting Grant Thoele, our current Chief of Staff to the CEO and Vice President of Corporate Strategy and Finance, to the position of Chief Financial Officer and Treasurer.

Mr. Thoele joined Aspen in August 2021 and has been crucial to the Company’s FP&A, Commercial Finance, and Corporate Strategy functions. Mr. Thoele brings extensive experience across strategic planning, process improvement, cost optimization, and corporate development activities. Prior to joining Aspen, Mr. Thoele was a Vice President at Providence Equity Partners, a global private equity firm specializing in strategic growth investments from April 2017 to August 2021. Mr. Thoele began his career in public accounting at KPMG, LLP in January 2011. Mr. Thoele received his Bachelor of Business Administration and Master of Science in Accounting from Texas Tech University.

There are no transactions to which we are a party and in which Mr. Thoele has a material interest that are required to be disclosed under Item 404(a) of Regulation S-K. Except as discussed above, Mr. Thoele has not previously held any positions with us, and Mr. Thoele has no family relationship with any of our directors or executive officers.

On August 4, 2025, we and Stephanie Pittman, our Chief Human Resources Officer and Corporate Secretary, determined that Ms. Pittman will depart the Company, effective as of October 1, 2025, to pursue other opportunities outside of the Company. Ms. Pittman’s departure is not related to any disagreement with the Company on any matter relating to the Company’s operations, policies or practices. We would like to thank Ms. Pittman for her valuable contributions to the Company.

We are conducting an external search for a Chief Administrative Officer position, which role is expected to lead the legal, compliance and human resources functions at the Company.

(c)10b5-1 Trading Plans

During the fiscal quarter ended June 30, 2025, the following directors and executive officers adopted a “rule 10b5-1 trading arrangement” (as defined in Item 408 of Regulation S-K of the Exchange Act).

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On June 3, 2025, Ricardo C. Rodriguez, Chief Financial Officer and Treasurer of the Company, adopteda Rule 10b5-1 Sales Plan (the "Plan"). Sales under the Plan may commence on September 2, 2025, after the completion of the required cooling off period under Rule 10b5-1. The Plan is intended to satisfy the affirmative defense of Rule 10b5-1(c) and provides for the sale of up to an aggregate of 25,353 shares of our common stock, plus the net number of shares of our common stock underlying certain restricted stock unit (“RSU”) awards, until September 30, 2026 (or earlier if all shares under the Plan have been sold). The number of shares to be sold pursuant to the Rule 10b5-1 trading arrangement is indeterminable with respect to the RSU awards, as such number is subject to the number of shares that will be automatically sold to satisfy applicable tax withholding obligations upon vesting of the RSU awards, which will vary based on the market price of our common stock at the time of vesting.

Except as disclosed above, none of our directors or executive officers adopted, modifiedor terminatedany 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 June 30, 2025.