Polysulfone (abbreviation PSU) is an amorphous plastic which, like polysulfone, is one of the high-temperature-resistant, high-performance thermoplastics.

PSU is an amorphous, transparent and pale yellow high-performance thermoplastic, similar to PES. It offers very good radiation resistance, good chemical and hydrolysis resistance and low levels of ionic impurities. It has a slightly lower temperature resistance than PES, but offers lower moisture absorption than PES, although drying is still required before thermoforming.

It has poor fatigue properties and is prone to environmental stress cracking, but has good long-term heat aging resistance. The chemical resistance is also very similar to that of PES.

The ignition temperature of polysulfone with an external flame is 475 °C. Combustion mainly produces CO2, SO2 and H2O, as well as other gases if there is little oxygen supply. Flame propagation speed and smoke development are low. For building materials, PSU was classified in building material class B2. The oxygen index according to ISO 4589 is 32%. Unreinforced power supplies were classified in class V1 according to UL94, reinforced power supplies with a thickness of 3,2 mm achieved V0.