<?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>0001457429</rptOwnerCik>
            <rptOwnerName>DABIERO CARMEN J</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 - Human Resources</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

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        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
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            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>408997</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
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    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Units 6/12/2009</value>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>268539</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>2.20</value>
                    <footnoteId id="F5"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            <expirationDate>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
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                <underlyingSecurityShares>
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            </underlyingSecurity>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options (to buy) 4/6/2004</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.15</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2013-03-18</value>
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            <transactionTimeliness>
                <value></value>
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                    <value>12500</value>
                </transactionShares>
                <transactionPricePerShare>
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                    <footnoteId id="F6"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            <exerciseDate>
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            <expirationDate>
                <value>2014-04-06</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
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                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>12500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
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        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options (to buy) 11/23/2008</value>
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            <conversionOrExercisePrice>
                <value>1.64</value>
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            <transactionDate>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>7500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.56</value>
                    <footnoteId id="F7"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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            <exerciseDate>
                <footnoteId id="F7"/>
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            <expirationDate>
                <value>2015-11-23</value>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>7500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options (to buy) 2/26/2009</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.66</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2013-03-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>47500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.54</value>
                    <footnoteId id="F8"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F8"/>
            </exerciseDate>
            <expirationDate>
                <value>2016-02-16</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>47500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
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        </derivativeTransaction>
    </derivativeTable>

    <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 800,000 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 268,539 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">This stock option, which provided for vesting upon grant, was cancelled in exchange for the right to receive the difference between the exercise price of the option and $2.20 per share in cash pursuant to the Merger Agreement.  These options 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="F7">This stock option, which provided for vesting 1/3rd on each of the first three anniversaries of the grant date was cancelled in exchange for the right to receive the difference between the exercise price of the option and $2.20 per share in cash pursuant to the Merger Agreement.  These options 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="F8">This stock option (which provided for vesting  over 33 months with prorated vesting on November 30, 2009, 2010 and 2011), was cancelled in exchange for the right to receive the difference between the exercise price of the option and $2.20 per share in cash pursuant to the Merger Agreement.  These options vested automatically immediately prior to the consummation of the merger on March 18, 2013 in accordance with the terms of the Merger Agreement.</footnote>
    </footnotes>

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