The invention relates to biaxially oriented polyester films which contain 0.1-5.0% by weight (based on the weight of the film) of a hydrolysis stabilizer based on epoxidized fatty acid esters and 0.2-10% by weight (based on the weight of the film) of epoxidized fatty acid glycerides, the epoxidized fatty acid esters having a mean molecular weight of at least 425 g/mol. Such films find use in outdoor applications, as a ribbon cable, as a backside laminate of solar modules and in electrical insulation applications.