Polystyrene (PS) is a thermoplastic polymer formed from styrene monomers, which contain an aromatic phenyl ring attached to a vinyl group. In the polymer, these phenyl rings become pendant side groups along the hydrocarbon backbone. The bulky aromatic side groups restrict chain movement, resulting in a material that is relatively rigid and dimensionally stable at room temperature but also more brittle than many other common thermoplastics. Polystyrene is typically amorphous, which contributes to its optical clarity in unfilled forms and allows it to be easily molded into precise shapes with good surface finish.
From a product design standpoint, polystyrene is valued for its ease of processing, low cost, and ability to reproduce fine detail in injection-molded parts. It is commonly used in disposable cutlery, appliance housings, packaging, lenses, and laboratory ware where stiffness and clarity are advantageous and high impact resistance is not required. Expanded polystyrene (EPS), produced by incorporating a blowing agent during processing, forms a lightweight cellular structure used extensively for thermal insulation and protective packaging. This illustrates how processing variations can significantly alter density and mechanical behavior while retaining the same base polymer chemistry.
Polystyrene is readily processed by injection molding, extrusion, and thermoforming, enabling efficient mass production of thin-walled and complex components. Designers often select polystyrene when dimensional accuracy, surface finish, and cost efficiency are primary considerations, and when the part will not be subjected to repeated impact or large flexural strains. Its relatively low heat resistance compared to some engineering plastics should be considered in applications exposed to elevated temperatures, but within its operating range it provides predictable stiffness, good electrical insulation, and compatibility with high-volume manufacturing methods.