A method for processing polyester wastes, especially used polyester bottles, which comprises shredding, washing, drying and melting the waste mixture to obtain a starting raw material wherein a modifying agent selected from the group comprising a combination of polysiloxane and a plasticizer selected from the group of phthalates, or a combination of silazanes and silanes is added to the shredded and dried waste mixture, the amount of the modifying agent being 4 to 6% by weight, based on the waste mixture.