Abstract: Extrusion foaming of neat PS and recycled PS with chemical materials as foaming agents was studied. Foaming behaviors of recycled PS using modified exothermic AC,modified endothermic NaHCO3, and exothermicendothermic composite blowing agents were compared regarding the density, cellular structure, and cellular uniformity of recycled PS foam. When the blowing agent content was 1 %, the density of the foam using AC and exothermicendothermic composite blowing agents was 0.47 g/cm3 and 0.39 g/cm3, respectively.