<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType><periodOfReport>2003-05-30</periodOfReport>
    <issuer>
        <issuerCik>0001101302</issuerCik>
        <issuerName>ENTEGRIS INC</issuerName>
        <issuerTradingSymbol>ENTG</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId>
            <rptOwnerCik>0001199621</rptOwnerCik>
            <rptOwnerName>WRIGHT MICHAEL WILLIAM</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>0</isDirector><isOfficer>1</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle>Chief Operating Officer</officerTitle></reportingOwnerRelationship></reportingOwner><derivativeSecurity><securityTitle><value>Stock Option (Right to Buy)</value></securityTitle><conversionOrExercisePrice><value>4.22</value></conversionOrExercisePrice><transactionDate><value>2003-05-30</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>S</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>17794</value></transactionShares><transactionValue><value>12.22</value></transactionValue><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>2000-09-06</value><footnoteId id="F1"/></exerciseDate><expirationDate><value>2009-09-06</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>19049</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>19049</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></derivativeSecurity><footnotes><footnote id="F1">17,794 shares are exercisable, and 19,049 shares will vest on June 7, 2003.</footnote></footnotes><ownerSignature><signatureName>Lori Cameron, Attorney-in-Fact for Michael W. Wright</signatureName><signatureDate>2003-06-03</signatureDate></ownerSignature></ownershipDocument>

