The thermal degradation of foamed polystyrene patterns in the expendable pattern casting (EPC) process has been studied. Various physical transitions that may occur during the degradation of the polymer have been determined with scanning electron microscopy, differential scanning calorimetry and thermogravimetric analysis. The effects of polymer density and bead structure on the degradation characteristics have been investigated. The results indicate that, when exposed to elevated temperatures, the polymer beads collapse at about 110-120 degrees C. The collapsed beads melt at 160 degrees C, and start to vaporize at temperatures greater than about 275 degrees C. Complete volatilization occurs in the temperature range 460-500 degrees C. The heat of degradation of expanded polystyrene has been estimated to be at the order of 912 J g(-1).