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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-03-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000748015</issuerCik>
        <issuerName>SEALY CORP</issuerName>
        <issuerTradingSymbol>ZZ</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001471818</rptOwnerCik>
            <rptOwnerName>ALLEN JODI</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O SEALY CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>ONE OFFICE PARKWAY</rptOwnerStreet2>
            <rptOwnerCity>TRINITY</rptOwnerCity>
            <rptOwnerState>NC</rptOwnerState>
            <rptOwnerZipCode>27370</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Sr VP-Marketing</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

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                <value>Common Stock</value>
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                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>375853</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
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    <derivativeTable>
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            <securityTitle>
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                <transactionPricePerShare>
                    <value>2.20</value>
                    <footnoteId id="F5"/>
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            <expirationDate>
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                    <value>33333</value>
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        <derivativeTransaction>
            <securityTitle>
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                <value>2013-03-18</value>
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                <value></value>
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                <transactionShares>
                    <value>70333</value>
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                <transactionPricePerShare>
                    <value>2.20</value>
                    <footnoteId id="F5"/>
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            <exerciseDate>
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            <expirationDate>
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                <underlyingSecurityTitle>
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    <footnotes>
        <footnote id="F1">Shares of Common Stock were disposed of in exchange for the right to receive $2.20 per share in cash pursuant to the Agreement and Plan of Merger by and among Tempur-Pedic International Inc., Silver Lightning Merger Company and Sealy Corporation (the &quot;Merger Agreement&quot;).</footnote>
        <footnote id="F2">Each restricted stock unit represented a contingent right to receive one share of Sealy Corporation common stock.</footnote>
        <footnote id="F3">The initial grant was for 400,000 restricted stock units with an annual growth rate of 8% until vested. One quarter of these units, plus accretion, vest on the first four anniversaries of the grant date. With the vesting on March 18, 2013, 130,831 units vested and the remaining units expired.</footnote>
        <footnote id="F4">The restricted stock units do not have an expiration date.</footnote>
        <footnote id="F5">Restricted stock units which were cancelled in exchange for the right to receive $2.20 per share in cash pursuant to the Merger Agreement.  These restricted stock units vested automatically immediately prior to the consummation of the merger on March 18, 2013 in accordance with the terms of the Merger Agreement.</footnote>
        <footnote id="F6">The initial grant was for 100,000 restricted stock units. The grant vests on an annual basis over 3 years.</footnote>
        <footnote id="F7">The initial grant was for 211,000 restricted stock units.  The grant vests on an annual basis over 3 years.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Kenneth L. Walker, by power of attorney</signatureName>
        <signatureDate>2013-03-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
