Expanded Polystyrene is a generic term for polystyrene and styrene copolymers that are expanded into a variety of useful products. EPS is supplied to molders in a resin form of polystyrene beads. EPS beads are loaded with a blowing agent, usually pentane, that gives the beads expansion vibrancy and allows them to be processed and molded into low-density foam articles. EPS is comprised of 90 percent air. The shock absorbing properties combined with its low cost, high insulating properties and custom moldability and ease of processing make it the most popular of the moldable foams.