ASPEN AEROGELS INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )

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Filed by a Party other than the Registrant ☐

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(Name of Registrant as Specified In Its Charter)

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Dear Aspen Aerogels, Inc. Stockholder:

You are cordially invited to attend the 2026 annual meeting of stockholders of Aspen Aerogels, Inc. to be held at 9:30 a.m. Eastern Time on Wednesday, May 13, 2026. This year’s annual meeting will be conducted solely via live audio webcast on the Internet.

You will be able to attend our annual meeting, vote and submit your questions during the annual meeting by visiting www.virtualshareholdermeeting.com/ASPN2026. You will not be able to attend the annual meeting in person.

Details regarding the meeting, the business to be conducted at the meeting, and information about Aspen Aerogels that you should consider when you vote your shares are described in the accompanying proxy statement.

At the 2026 annual meeting, two persons will be elected to our Board of Directors. In addition, we ask stockholders to ratify the appointment of KPMG LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2026, to approve, on a non-binding, advisory basis, the compensation of the named executive officers, as disclosed in the accompanying proxy statement for the 2026 annual meeting of stockholders, to vote, on a non-binding, advisory basis, on the frequency of holding an advisory vote on the compensation of our named executive officers, and to consider, on a non-binding, advisory basis, a proposal regarding future declassification of our Board of Directors. Our Board of Directors recommends the election of the two nominees to our Board of Directors, a vote in favor of proposals (2), (3) and (5), and a vote for “One Year” on proposal (4). Such other business will be transacted as may properly come before the annual meeting.

Under Securities and Exchange Commission rules that allow companies to furnish proxy materials to stockholders over the Internet, we have elected to deliver our proxy materials to the majority of our stockholders over the Internet. This delivery process allows us to provide stockholders with the information they need, while at the same time conserving natural resources and lowering the cost of delivery. On or about March 27, 2026, we will send to our stockholders a Notice of Internet Availability of Proxy Materials (the “Notice”) containing instructions on how to access our proxy statement for our 2026 annual meeting of stockholders and our 2025 annual report to stockholders. The Notice also provides instructions on how to vote online and includes instructions on how to receive a paper copy of the proxy materials by mail.

We hope you will be able to attend the annual meeting. Whether you plan to attend the annual meeting or not, it is important that you cast your vote. Prior to the annual meeting, you may vote by proxy over the Internet as well as by telephone or by mail. When you have finished reading the proxy statement, you are urged to vote in accordance with the instructions set forth in the proxy statement. We encourage you to vote by proxy so that your shares will be represented and voted at the meeting, whether or not you can attend. Any stockholder attending the virtual annual meeting may vote online during the annual meeting, even if you already returned a proxy card or voted by proxy over the telephone or the Internet.

Thank you for your continued support of Aspen Aerogels, Inc. We look forward to seeing you at the annual meeting.

Sincerely,

President and Chief Executive Officer

NOTICE OF 2026 ANNUAL MEETING OF STOCKHOLDERS

TIME: 9:30 a.m. Eastern Time

DATE: Wednesday, May 13, 2026

ACCESS: www.virtualshareholdermeeting.com/ASPN2026

This year’s annual meeting will be a virtual meeting via live webcast on the Internet. You will be able to attend the annual meeting, vote and submit your questions during the meeting by visiting www.virtualshareholdermeeting.com/ASPN2026 and providing relevant information, including the control number included in the Notice of Internet Availability or the proxy card or voting instruction form that you received. For further information, please see the Important Information About the Annual Meeting and Voting beginning on page 4 of this proxy statement.

PURPOSES:

To elect Steven R. Mitchell and Donald R. Young as directors to serve three-year terms expiring in 2029;

To ratify the appointment of KPMG LLP as Aspen Aerogels, Inc.’s independent registered public accounting firm for the fiscal year ending December 31, 2026;

To approve, on a non-binding, advisory basis, the compensation of the named executive officers, as disclosed in our proxy statement for the annual meeting;

To approve, on a non-binding, advisory basis, the frequency of holding an advisory vote on the compensation of the named executive officers;

To consider, on a non-binding, advisory basis, a proposal regarding the future declassification of the Board of Directors; and

To transact such other business that is properly presented at the annual meeting and any adjournments or postponements thereof.

WHO MAY VOTE:

You may vote if you were the record owner of Aspen Aerogels, Inc.’s common stock at the close of business on March 16, 2026 (the “Record Date”). A list of registered stockholders as of the close of business on the Record Date will be available at our corporate headquarters for examination by any stockholder for any purpose germane to the annual meeting for a period of 10 days ending on the day before the date of the annual meeting. If you wish to view this list, please contact our Corporate Secretary at Aspen Aerogels, Inc., 30 Forbes Road, Building B, Northborough, Massachusetts 01532.

All stockholders are cordially invited to attend the virtual annual meeting. Whether you plan to attend the annual meeting or not, we urge you to vote by following the instructions in the Notice of Internet Availability of Proxy Materials or proxy materials you received and submit your proxy by the Internet, telephone or mail in order to ensure the presence of a quorum. You may change or revoke your proxy at any time before it is voted at the meeting.

By Order of the Board of Directors,

Glenn E. Deegan

Chief Administrative Officer, General Counsel & Corporate Secretary

CREATING VALUE THROUGH TECHNOLOGY, INNOVATION, AND EXECUTION

Dear Stakeholders,

In 2025, we remained focused on our core objective of building a strong, profitable, and capital-efficient business. During the year, we streamlined the organization, optimized our cost structure, and reduced structural expenses while strengthening operational discipline. These actions bolstered the foundation of the business while preserving the capabilities needed to support sustainable, long-term growth and value creation.

Our Energy Industrial business continued to provide important diversification, supported by long-standing customer relationships across global energy infrastructure markets. While 2025 was weighted toward maintenance activity and reflected fewer large subsea projects than in prior years, the fundamentals of the business remain strong. As 2026 begins, visibility has improved and three structural drivers are supporting growth: a rebound in subsea project activity, expanding LNG and natural gas infrastructure investment, and steady maintenance demand from refinery and petrochemical operators. We have already secured subsea and LNG project awards for 2026, and our pipeline is strong. We believe our Energy Industrial segment can continue to grow as a high-margin business without significant incremental costs or capital investment.

Within our Thermal Barrier business, EV production decreased in North America during the year as OEMs adjusted volumes in response to evolving regulatory frameworks and market demand. We expect the market to establish a new baseline in 2026, from which EV penetration can resume growth at a steadier pace. In Europe, structural drivers create a more visible multi-year adoption trajectory for OEMs. We are actively engaged with several European OEMs as they advance to their next-generation EV platforms, and we anticipate securing additional awards. This foundation positions us well for growth beginning in 2027 and provides greater geographic and customer diversification over time.

We are also pursuing the extension of the Aerogel Technology Platform® into adjacent markets where our thermal management and fire protection capabilities address critical needs. Battery energy storage systems represent one such opportunity, as stationary storage installations increase in scale and energy density. Our thermal protection capabilities and U.S.-based manufacturing footprint position us well in this evolving market. We continue to evaluate additional applications that leverage our manufacturing scale and technical expertise.

Throughout 2025, we strengthened our balance sheet and managed cash with discipline. We ended the year with approximately $159 million in cash and cash equivalents and expect to receive nearly $38 million from General Motors in Q1 2026 related to a commercial settlement. We removed approximately $75 million of structural fixed costs on an annualized basis and materially lowered our adjusted EBITDA breakeven level. Expected Plant II asset sales in 2026 will further reduce debt and strengthen our balance sheet. These actions enhance liquidity and financial flexibility while increasing operating leverage as revenue grows.

As we look ahead, our focus remains clear: execute consistently, allocate capital thoughtfully, and build a stronger company positioned to deliver sustainable, long-term value.

2025 Highlights and Recent Business Developments

•

Awarded North Sea pipe-in-pipe subsea project with expected delivery in Q3 2026

•

Supported several LNG projects as part of an expanding gas infrastructure portfolio

•

Awarded PyroThin® Thermal Barrier contract from Volvo Cars with expected start of production in 2027

•

Awarded PyroThin contract from a leading American OEM for a vehicle platform with expected start of production in 2028

•

Removed approximately $75 million of structural fixed costs, materially lowering EBITDA breakeven

•

Ended 2025 with approximately $159 million in cash; expect nearly $38 million GM payment in Q1 2026

•

Pursuing sale of Plant II assets to further strengthen the balance sheet

We believe Aspen Aerogels is well positioned for the years ahead. Demand for high-performance thermal and energy-efficiency solutions continues to be supported by long-term trends in electrification, energy infrastructure, safety standards, and sustainability. With a differentiated technology platform, expanding customer relationships, and a more efficient cost structure, we remain focused on delivering profitable growth and building long-term shareholder value.

I would like to thank our employees for their dedication and professionalism, and our customers and partners for their continued trust. We also appreciate the support of our shareholders and look forward to updating you on our progress in the year ahead.

Sincerely,

President & Chief Executive Officer

TABLE OF CONTENTS

PROXY STATEMENT FOR THE ASPEN AEROGELS, INC.

2026 ANNUAL MEETING OF STOCKHOLDERS TO BE HELD ON MAY 13, 2026

This proxy statement, along with the accompanying notice of 2026 annual meeting of stockholders, contains information about the 2026 annual meeting of stockholders of Aspen Aerogels, Inc., including any adjournments or postponements of the annual meeting. We are holding the annual meeting at 9:30 a.m. Eastern Time on Wednesday, May 13, 2026. This year’s annual meeting will be conducted solely via live audio webcast on the Internet. You will be able to attend our annual meeting, vote and submit your questions during the annual meeting by visiting www.virtualshareholdermeeting.com/ASPN2026. You will not be able to attend the annual meeting in person.

In this proxy statement, we refer to Aspen Aerogels, Inc. as “Aspen Aerogels,” “the Company,” “we,” “our” and “us.”

This proxy statement relates to the solicitation of proxies by our Board of Directors (the “Board of Directors” or the “Board”) for use at the annual meeting.

On or about March 27, 2026, we intend to begin sending to our stockholders entitled to vote at the annual meeting the Notice of Internet Availability of Proxy Materials containing instructions on how to access our proxy statement for the 2026 annual meeting of stockholders and our 2025 annual report. Stockholders who have previously requested to receive paper copies of our proxy materials will receive paper copies of the proxy materials instead of a Notice of Internet Availability.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE ANNUAL STOCKHOLDER MEETING TO BE HELD ON MAY 13, 2026

This proxy statement and our 2025 annual report to stockholders are available for viewing, printing and downloading at www.proxyvote.com. In order to view, print or download these materials, please have the 16-digit control number(s) that appears on your notice or proxy card available. On this website, you can also elect to receive future distributions of our proxy statements and annual reports to stockholders by electronic delivery.

Additionally, you can find a copy of our Annual Report, which includes our financial statements, for the fiscal year ended December 31, 2025 on the website of the Securities and Exchange Commission, or the SEC, atwww.sec.gov, or in the “SEC Filings” tab of the “Financials” subsection of the “Investors” section of our website at www.aerogel.com. You may also obtain a printed copy of our Annual Report, including our financial statements, from us, free of charge, by sending a written request to:

Attn: Investor Relations

Exhibits will be provided upon written request and payment of an appropriate processing fee.