Abstract In this paper, a self designed gas foaming apparatus which differs from the existing ones has been introduced. It consists of a high pressure gas supply system, high pressure mold, molding machine, pressure gauge and gas release valve. Each parameter of the apparatus was carefully evaluated and tested. The results showed that the temperature, pressure and depressurization rate can be accurately controlled. Due to the precise control of foaming parameters, the raw resins of low density polyethylene (LDPE) and polypropylene (PP) were successfully foamed with nitrogen (N 2) as a blowing agent. The foamed samples had an expansion ratio as high as 20 times and had an average diameter below 140.0 μm. The cell structure was uniform throughout the sample.