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( Mark One ) ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR 0 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number : 001-36481 ASPEN AEROGELS , INC . ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of incorporation or organization ) 30 Forbes Road , Building B Northborough , Massachusetts ( Address of principal executive offices ) Large accelerated filer Non - accelerated filer Title of each class Common Stock , par value $ 0.00001 per share Registrant's telephone number , including area code ( 508 ) 691-1111 Securities registered pursuant to Section 12 ( b ) of the Exchange Act : Trading Symbol 04-3559972 ( I.R.S. Employer Identification No. ) ASPN 01532 ( Zip Code ) Name of exchange on which registered New York Stock Exchange Securities registered pursuant to Section 12 ( g ) of the Exchange Act : None Yes ☐ No ㄖ Yes ☐ No " Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Exchange Act . Indicate by check mark whether the registrant ( 1 ) has filed all reports required be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes - No Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( §232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of “ large accelerated filer ” , “ accelerated filer , ” “ smaller reporting company , ” and “ emerging growth company " in Rule 12b - 2 of the Exchange Act . Accelerated filer Smaller reporting company Emerging growth company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . □ ☐ > > Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . Yes No Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . The aggregate market value of the registrant's common stock held by non - affiliates of the registrant ( without admitting that any person whose shares are not included in such calculation is an affiliate ) computed by reference to the price at which the common stock was last sold as of the last business day of the registrant's most recently completed second fiscal quarter was approximately $ 169.5 million . As of March 9 , 2021 , the registrant had 28,301,338 shares of common stock outstanding . DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant's definitive Proxy Statement for its Annual Meeting of Stockholders to be held on June 1 , 2021 are incorporated by reference into Part III of this Annual Report on Form 10 - K to the extent stated herein .