Polystyrene (PS) plastic is a naturally transparent thermoplastic that is available as both a typical solid plastic as well in the form of a rigid foam material. PS is used in a wide variety of industries and applications such as toys, household appliances, Automotive, electronics, medical, etc. General Purpose Polystyrene (GPPS) and High Impact Polystyrene (HIPS) are the most common uses PS resins for injection molding. GPPS is clear, but brittle (think of a CD jewel case) while HIPS is opaque and much less brittle.