General Purpose Polystyrene (GPPS), known as "crystal" in commercial systems, finds a wide range of applications due to its suitability for injection molding and heat shaping, affordability, high light transmittance, and excellent shape stability.

A distinctive advantage of polystyrene over other thermoplastics is its amorphous structure. It transitions from a glassy state to a molten state with minimal energy expenditure. The absence of crystallization energy allows for rapid heating and cooling, thus providing the advantage of quick molding. It can be easily molded without degradation using low energy through extrusion and injection molding methods. The amorphous nature of polystyrene results in very little shrinkage during molding compared to crystalline plastics like polyethylene and polypropylene. Polystyrene also has the best electrical insulation properties among all polymer types, with a dielectric constant that remains constant between temperatures of 20–80°C.

GPPS is used in various fields including the production of disposable cups, plates, cutlery, toys, appliance parts, medical packaging, glassware, food packaging, foam insulation boards, CD cases, cosmetic packaging, hangers, toy components, watch casings, and promotional materials.