Expanded polystyrene is a plastic foam made of tiny interconnected beads. During the manufacturing process, pentane gas is blown into the foam to achieve the finished product.
According to the Extruded Polystyrene Foam Association, this type of polystyrene is manufactured under extremely hot temperatures and pressure. After it cools, it is cut into the desired shape and size. Extruded polystyrene is used for commercial and residential insulation,and also to make items such as plastic foam cups and plates.
Both variations of polystyrene are rigid thermoplastic foam products. However, due to the different ways they are manufactured, extruded polystyrene is a better insulator and does not adsorb as much moisture as expanded polystyrene. According to the Expanded Polystyrene Molders Association, expanded polystyrene is an ideal soundproofing material and a good choice for environmentally-conscious builders.