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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-04-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001288738</rptOwnerCik>
            <rptOwnerName>KKR Millennium GP LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001358535</rptOwnerCik>
            <rptOwnerName>Sealy Holding LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001288736</rptOwnerCik>
            <rptOwnerName>KKR Millennium Fund L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001288737</rptOwnerCik>
            <rptOwnerName>KKR Associates Millennium L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001081714</rptOwnerCik>
            <rptOwnerName>KRAVIS HENRY R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001081715</rptOwnerCik>
            <rptOwnerName>ROBERTS GEORGE R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001205970</rptOwnerCik>
            <rptOwnerName>GREENE JAMES H JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001192062</rptOwnerCik>
            <rptOwnerName>RAETHER PAUL E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001182415</rptOwnerCik>
            <rptOwnerName>MICHELSON MICHAEL W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001206581</rptOwnerCik>
            <rptOwnerName>GOLKIN PERRY</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O KOHLBERG KRAVIS ROBERTS &amp; CO. L.P.</rptOwnerStreet1>
            <rptOwnerStreet2>9 WEST 57TH STREET, SUITE 4200</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common stock, par value $0.01 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2006-04-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3481868</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>16.00</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>46625921</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents price to the public pursuant to an underwritten initial public offering before underwriting discounts.</footnote>
        <footnote id="F2">These securities are held of record by Sealy Holding LLC. As senior member of Sealy Holding LLC, KKR Millennium Fund L.P. may be deemed a beneficial owner of such shares of common stock of the Issuer held by Sealy Holding LLC. As the sole general partner of KKR Millennium Fund L.P., KKR Associates Millennium L.P. may be deemed to be the beneficial owner of such shares of common stock of the Issuer held by Sealy Holding LLC. As the sole general partner of KKR Associates Millennium L.P., KKR Millennium GP LLC also may be deemed to be the beneficial owner of such shares of common stock of the Issuer held by Sealy Holding LLC.</footnote>
        <footnote id="F3">The members of KKR Millennium GP LLC are Henry R. Kravis, George R. Roberts, James H. Greene, Jr., Paul E. Raether, Michael W. Michelson, Perry Golkin, Johannes P. Huth, Todd A. Fisher, Alexander Navab, Marc S. Lipschultz, Reinhard Gorenflos, Jacques Garaialde, Michael M. Calbert and Scott C. Nuttall, and as such, may be deemed to share beneficial ownership of any shares of common stock of the Issuer that KKR Millennium GP LLC may be deemed to beneficially own. Each Reporting Person, other than Sealy Holding LLC, disclaims beneficial ownership of these securities, except to the extent of its or his pecuniary interest therein.</footnote>
        <footnote id="F4">The filing of this statement shall not be deemed and admission that, for purposes of Section 16 of the Securities Exchange Act of 1934 or otherwise, the Reporting Person is the beneficial owners of all such equity securities covered by this statement.</footnote>
        <footnote id="F5">Due to limitations on Form 4, certain of the persons described as beneficial owners or deemed beneficial owners of the securities reported on this Form 4 are filing as reporting persons on separate Forms 4.</footnote>
    </footnotes>

    <remarks>Exhibit 24 - Power of Attorney (previously filed); Exhibit 99 - Joint Filer Information</remarks>

    <ownerSignature>
        <signatureName>/s/ William J. Janetschek by power of attorney for Reporting Person</signatureName>
        <signatureDate>2006-04-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
