Com. polyamide and polypropylene were modified by addn. of a blowing agent (1% by mass) and glass and C fiber fillers (15 and 30% by mass). The effect of additives on mass, thickness, hardness and tensile strength as well as on the structure of composite moldings was studied. The addn. of the blowing agent resulted in a decrease in mass, hardness and tensile strength of the test pieces, while the addn. of the fillers resulted in an improvement of the properties.