Like Polyetherimide (PEI), its properties are somewhat inferior to PEEK and it is less expensive. Polyethersulphone has a slightly higher temperature resistance than PEI (but less than PEEK) and is the most temperature resistant transparent commercially available thermoplastic. It has a relatively high water absorption and, in common with many other plastics, drying is essential before thermoforming. Polyethersulphone has poor fatigue characteristics and is prone to environmental stress cracking but has good long term thermal ageing resistance and reasonable radiation resistance. Its chemical resistance is not as wide as PEEK's.