Because HIPS is flammable and produces a large amount of black smoke when burning, the added flame retardants must consider not only their flame retardancy but also their smoke suppression function. Currently, the main flame retardants used in HIPS include organic brominated flame retardants such as tetrabromobisphenol A(TBBPA), decabromodiphenyl ether (DBDPO), OBDPO, BTPE, CPE, ATO, and zinc oxide (ZnO). Magnesium hydroxide and aluminum hydroxide have good flame retardant and smoke suppression functions and are widely used.

For halogen-free flame-retardant HIPS, organophosphorus, metal oxide, and metal hydroxide flame retardants are generally preferred. Commonly used ammonium polyphosphate (APP), MPP, aluminum hypophosphite (ALHP), aluminum diethylphosphite (ADP), and MCA have poor flame retardant effects in HIPS and are not recommended.