•Expanded polystyrene (EPS) is a rigid closed cell/cellular plastic resin made from petrochemicals derived from crude oil. The resin is incorporated with the blowing agent pentane. During the pre-expansion, steam softens the plastic resin causing the pentane to expand the plastic into beads at least 100 times their original size. •As long as the plastic is exposed to steam, the longer the pentane expands, therefore determining the expanded size of the bead. Before all of the pentane is displaced by air, the pre-expanded bead is then placed into a mold of any shape or block.