It has excellent high temperature properties – probably on balance the best of any commercially available polymer – and is very expensive. It is strong, stiff, very hard, has a particularly high strength in and recovery from compression and a CTE similar to that of aluminium. It has good chemical resistance resisting many harsh chemical environments better than many other high performance polymers, but is attacked by polar aprotic solvents and, at elevated temperatures, by strong aqueous acids and (to a lesser extent) alkalis. Despite absorbing (slowly) a high percentage of water at saturation, it is stable to hydrolysis and resists high pressure steam.