Six waste polyolefins of various origin were studied for mech. properties and used for prodn. of plastic foams by crosslinking under foaming at 183 degrees C and 22 MPa for 5 min as received or in blends with com. copolymers CH2=CH2/AcOCH=CH2 or CH2=CH2/CH2=CHCOOH. The best secondary raw material for foaming was a low-d. polyethylene waste.