The melting point (200-210 °C) refers to the melting temperature of the crystalline part. However, PS is essentially an amorphous polymer, and the "glass transition temperature (Tg)" is more commonly used to measure its heat resistance. Its Tg is approximately 80-105 °C. This means that when the temperature exceeds Tg, PS will change from a hard "glassy state" to a soft "highly elastic state". Thus, the recommended long-term service temperature is not more than 60-70 °C; otherwise, it is prone to deformation.

It has poor flame retardancy and is flammable when exposed to fire. During combustion, it releases black smoke and styrene monomers (with an irritating odor), so fire safety precautions must be taken.