(10) Stock-Based Compensation

During the six months ended June 30, 2026, the Company granted 382,441 restricted stock units (RSUs) with an aggregate grant date fair value of $1.3 million, non-qualified stock options (NSOs) to purchase 517,961 shares of common stock with an aggregate grant date fair value of $1.3 million and 764,886 performance share units (PSUs) with an aggregate grant date fair value of $4.2 million to employees under its equity incentive plans. The RSUs and NSOs granted to employees will typically vest over a three-year period, subject to continued service. Vesting of any performance share units so earned generally is also contingent upon the grantee’s continued employment (or other service) with the Company through the third anniversary of the date of grant.

During the six months ended June 30, 2026, the Company also granted RSUs that vest over a period of three years which are settled in cash. The Company has accounted for the RSUs settled in cash as liability-classified awards and accordingly changes in the market value of the instruments will be recorded to cost of revenue or operating expense, as applicable, over the vesting period of the award. The fair value of a liability-classified award is determined on a quarterly basis beginning at the grant date until final vesting. These awards will be settled on the vesting dates and the maximum liability is capped at 200% of the fair value of the award at the grant date. During the three and six months ended June 30, 2026, the Company incurred expenses of $1.8 million and $2.3 million, respectively, for the liability-classified awards. During the three and six months ended June 30, 2025, the Company incurred expenses of $0.4 million and $0.5 million, respectively, for the liability-classified awards. At June 30, 2026 and December 31, 2025, the fair value of these awards were $2.4 million and $0.5 million, respectively.

During the six months ended June 30, 2026, the Company also granted 51,850 RSUs with a grant date fair value of $0.3 million and NSOs to purchase 43,530 shares of common stock with a grant date fair value of $0.2 million to its non-employee directors under the 2023 Plan (as defined below). The RSUs and NSOs granted to non-employee directors will typically vest over a one-year period.

The Company’s stockholders approved the Aspen Aerogels Amended and Restated 2023 Equity Incentive Plan (the 2023 Plan) at the Company's 2025 Annual Meeting of Stockholders held on April 30, 2025 (the 2025 Annual Meeting). The 2023 Plan was previously approved by the Company’s Board of Directors (the Board). As amended and restated, the number of shares of the Company’s common stock reserved for issuance under the 2023 Plan was increased by 3,850,000 shares to 16,971,994 shares and the term of the 2023 Plan was extended until April 29, 2035. As of June 30, 2026, 5,435,213 shares of common stock were reserved for issuance upon the exercise or vesting of outstanding stock-based awards granted under the Company’s equity incentive plans. Any cancellations or forfeitures of awards outstanding under the 2023 Plan, the Company's 2014 Employee, Director and Consultant Equity Incentive Plan or the Company's 2001 Equity Incentive Plan, as amended, will result in the shares reserved for issuance pursuant to such awards becoming available for grant under the 2023 Plan. As of June 30, 2026, the Company has either reserved in connection with statutory tax withholdings or issued a total of 6,976,559 shares under the Company’s equity incentive plans. As of June 30, 2026, there were 4,560,222 shares of common stock available for future grant under the 2023 Plan.

At the 2025 Annual Meeting, the Company’s stockholders also approved the Aspen Aerogels Employee Stock Purchase Plan (the ESPP). The ESPP was previously approved by the Board. The objective of the ESPP is to offer eligible employees of the Company and its designated subsidiaries the ability to purchase shares of the Company’s common stock at a 15% discount from the fair market value of the stock as determined on specific dates at six-month intervals, subject to various limitations under the ESPP. 4,000,000 shares of the Company’s common stock are authorized for issuance under the ESPP. The offering periods for the ESPP generally start on the first trading day on or after June 1st and December 1st of each year. The first offering period for the ESPP commenced on the first trading day after June 1, 2025 and ended on November 30, 2025, the second offering period commenced on the first trading day after December 1, 2025 and ended on May 31, 2026, and the third offering period commenced on June 1, 2026 and will end on November 30, 2026. During the three and six months ended June 30, 2026, less than $0.1 million and $0.1 million of stock-based compensation was recognized for the ESPP, respectively. During each of the three and six months ended June 30, 2025, less than $0.1 million of stock-based compensation was recognized for the ESPP.

The Company recognizes forfeitures on share-based payments as they occur. During the three and six months ended June 30, 2026, total stock-based compensation includes $0.1 million and $0.2 million for forfeitures recorded, respectively. During the three and six months ended June 30, 2025, total stock-based compensation included ($0.8) million and ($1.7) million for forfeitures recorded, respectively.