Polystyrene (PS) - Polystyrene is an amorphous, glassy polymer that is generally rigid and relatively inexpensive. Unfilled polystyrene has a sparkle appearance and is often referred to as crystal PS or general purpose polystyrene (GPPS). High impact polystyrene grades (HIPS) are produced by adding rubber or butadiene copolymer which increases the toughness and impact strength of the polymer. Polystyrenes possess good flow properties at temperatures safely below degradation ranges, and can easily be extruded, injection molded, or compression molded. Considerable quantities of polystyrene are produced in the form of heat-expandable beads containing a suitable blowing agent which ultimately results in familiar foamed polystyrene articles.