Foamed polymer composition comprising polystyrene and polyethyleneterephthalate

An expanded extruded polystyrene sheet is described, containing 0.5% to 3% polyethyleneterephthalate (PET) by weight of the polystyrene weight and /exhibiting an integral compact layer on at least one of its surfaces, as well as a method for the production of said sheet comprising the steps of forming a mixture comprising polystyrene and 0.5%-3% of (PET), melting the mixture by heating inside an extruder, adding a blowing agent to the melt mixture and extruding the mixture in an environment at lower pressure through a die, cooling the sheet on exit from the die on at least one of its surfaces by means of air blow.