content: <?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
    <!-- Generated by Workiva -->
    <headerData>
      <submissionType>144</submissionType>
      <filerInfo>
        <filer>
          <filerCredentials>
            <cik>0001610257</cik>
            <ccc>XXXXXXXX</ccc>
          </filerCredentials>
        </filer>
        <liveTestFlag>LIVE</liveTestFlag>
  
  
  
      </filerInfo>
    </headerData>
    <formData>
      <issuerInfo>
        <issuerCik>0001145986</issuerCik>
        <issuerName>Aspen Aerogels, Inc.</issuerName>
        <secFileNumber>001-36481</secFileNumber>
        <issuerAddress>
          <com:street1>30 Forbes Road, Building B</com:street1>
          <com:city>Northborough</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>01532</com:zipCode>
        </issuerAddress>
        <issuerContactPhone>508-691-1111</issuerContactPhone>
        <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>Donald R. Young</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
        <relationshipsToIssuer>
          <relationshipToIssuer>President, CEO, Director</relationshipToIssuer>
        </relationshipsToIssuer>
      </issuerInfo>
      <securitiesInformation>
        <securitiesClassTitle>Common Stock</securitiesClassTitle>
        <brokerOrMarketmakerDetails>
          <name>J.P. Morgan Securities LLC</name>
          <address>
            <com:street1>390 Madison Avenue</com:street1>
            <com:street2>6th Floor</com:street2>
            <com:city>New York</com:city>
            <com:stateOrCountry>NY</com:stateOrCountry>
            <com:zipCode>10017</com:zipCode>
          </address>
        </brokerOrMarketmakerDetails>
        <noOfUnitsSold>134629</noOfUnitsSold>
        <aggregateMarketValue>3718452</aggregateMarketValue>
        <noOfUnitsOutstanding>77082075</noOfUnitsOutstanding>
        <approxSaleDate>09/30/2024</approxSaleDate>
        <securitiesExchangeName>NYSE</securitiesExchangeName>
      </securitiesInformation>
      <securitiesToBeSold>
        <securitiesClassTitle>Common Stock</securitiesClassTitle>
        <acquiredDate>08/08/2023</acquiredDate>
        <natureOfAcquisitionTransaction>Open Market Purchase</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>See Nature of Acquistion</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>25000</amountOfSecuritiesAcquired>
        <paymentDate>08/08/2023</paymentDate>
        <natureOfPayment>Cash</natureOfPayment>
      </securitiesToBeSold>
      <securitiesToBeSold>
        <securitiesClassTitle>Common Stock</securitiesClassTitle>
        <acquiredDate>05/12/2022</acquiredDate>
        <natureOfAcquisitionTransaction>Open Market Purchase</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>See Nature of Acquistion</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>5000</amountOfSecuritiesAcquired>
        <paymentDate>05/12/2022</paymentDate>
        <natureOfPayment>Cash</natureOfPayment>
      </securitiesToBeSold>
      <securitiesToBeSold>
        <securitiesClassTitle>Common Stock</securitiesClassTitle>
        <acquiredDate>02/28/2019</acquiredDate>
        <natureOfAcquisitionTransaction>Compensation</natureOfAcquisitionTransaction>
        <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
        <isGiftTransaction>N</isGiftTransaction>
        <amountOfSecuritiesAcquired>104629</amountOfSecuritiesAcquired>
        <paymentDate>02/26/2023</paymentDate>
        <natureOfPayment>Compensation</natureOfPayment>
      </securitiesToBeSold>
      <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
      <remarks>The shares covered by this filing will be sold by Donald and Caroline Young acting jointly.  Also, 140,629 of the shares to be sold were acquired from compensation received during the period of 02/28/19 and 02/26/23.</remarks>
      <noticeSignature>
        <noticeDate>09/30/2024</noticeDate>
        <planAdoptionDates>
          <planAdoptionDate>06/04/2024</planAdoptionDate>
        </planAdoptionDates>
        <signature>/s/ J.P. Morgan Securities LLC as agent and attorney-in-fact for Donald R. Young</signature>
      </noticeSignature>
    </formData>
  </edgarSubmission>
metadata_documents: [{"type": "144", "sequence": "1", "filename": "primary_doc.xml", "secsgml_size_bytes": 4336}]
text: 144
  0001610257
  XXXXXXXX
  LIVE
  0001145986
  Aspen Aerogels, Inc.
  001-36481
  30 Forbes Road, Building B
  Northborough
  MA
  01532
  508-691-1111
  Donald R. Young
  President, CEO, Director
  Common Stock
  J.P. Morgan Securities LLC
  390 Madison Avenue
  6th Floor
  New York
  NY
  10017
  134629
  3718452
  77082075
  09/30/2024
  NYSE
  Common Stock
  08/08/2023
  Open Market Purchase
  See Nature of Acquistion
  N
  25000
  08/08/2023
  Cash
  Common Stock
  05/12/2022
  Open Market Purchase
  See Nature of Acquistion
  N
  5000
  05/12/2022
  Cash
  Common Stock
  02/28/2019
  Compensation
  Issuer
  N
  104629
  02/26/2023
  Compensation
  Y
  The shares covered by this filing will be sold by Donald and Caroline Young acting jointly.  Also, 140,629 of the shares to be sold were acquired from compensation received during the period of 02/28/19 and 02/26/23.
  09/30/2024
  06/04/2024
  /s/ J.P. Morgan Securities LLC as agent and attorney-in-fact for Donald R. Young