The application discloses a transparent, biaxially oriented polyester film having a base layer at least 80% by weight of which is composed of a thermoplastic polyester, and having at least one outer layer, wherein the outer layer is composed of a copolymer or of a mixture of polymers which comprises at least 35 mol % of ethylene 2,6-naphthalate units, up to 44 mol % of ethylene terephthalate units, and from 1 to 20 mol % of ethylene isophthalate units, and also up to 20 mol % of a sulfo-substituted dicarboxylic acid and, if desired, up to 10 mol % of units from aliphatic, including cycloaliphatic, or aromatic diols and/or dicarboxylic acids (based in each case on the total content of dicarboxylic acid or diol).