<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-02-21</periodOfReport>

    <issuer>
        <issuerCik>0000914156</issuerCik>
        <issuerName>UFP TECHNOLOGIES INC</issuerName>
        <issuerTradingSymbol>UFPT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001240682</rptOwnerCik>
            <rptOwnerName>SHAW DANIEL J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O UFP TECHNOLOGIES, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>100 HALE STREET</rptOwnerStreet2>
            <rptOwnerCity>NEWBURYPORT</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01950</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $.01 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2018-02-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>966</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16692</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $.01 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2018-02-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1280</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17972</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents stock unit awards granted on February 21, 2017, under the issuer's 2003 Incentive Plan subject to satisfaction of performance targets that are to be settled solely in shares of common stock. The transaction date represents the date on which the issuer's Compensation Committee determined the performance targets were achieved. The units vest with respect to one-third of the shares on March 1, 2019 and with respect to an additional one-third on each of March 1, 2020 and 2021, so long as the recipient is in the continuous employ of the Issuer through each such respective vesting date.</footnote>
        <footnote id="F2">Represents stock unit awards granted on February 21, 2018, under the issuer's 2003 Incentive Plan the vesting under which is soley time-based, that are to be settled solely in shares of common stock. The units vest with respect to one-third of the shares on March 1, 2020 and with respect to an additional one-third on each of March 1, 2021 and 2022, so long as the recipient is in the continuous employ of the Issuer through each such respective vesting date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Patrick J. Kinney, Jr. as attorney-in-fact for Daniel J. Shaw</signatureName>
        <signatureDate>2018-02-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
