PES (Polyethersulfone) (Ultrason®) is a transparent, heat resistant, high performance engineering thermoplastic. PES is a strong, rigid, ductile material with excellent dimensional stability. It has good electrical properties and chemical resistance. PES can withstand prolonged exposure to elevated temperatures in air and water. PES is used in electrical applications, pump housings, and sight glasses. The material can also be sterilized for use in medical and food service applications. Along with some other plastics such as PEI (Ultem®), it is relatively transparent to radiation.