Invention relates to a process for producing a single-layer or multilayer film by extrusion or coextrusion, biaxial orientation, and heat setting based on crystallizable thermoplastics whose principal constituent is a crystallizable thermoplastic having a standard viscosity SV (DCA) of from 600 to 1000. The thermoplastic is mixed prior to extrusion or coextrusion with 50% by weight (based on the total weight of all thermoplastics) of a secondary thermoplastic having a standard viscosity SV (DCA) of more than 900 to 1500, the standard viscosity SV (DCA) of the two thermoplastics differing by at least 100 units. The secondary thermoplastic is a byproduct or waste product from the production of PET plastic bottles or originates from recycled PET bottles.