The materials defined by these specifications are thermoplastic elastomers of nominal instantaneous Durometer ‘A’ hardnesses ranging from 60 to 89 having good long term resistance to heat and engine coolant at temperatures up to 125 °C. The harder materials also have moderate resistance to oil. Resistance to other fluids cannot be assumed without further testing. Being thermoplastic, the material will soften and creep at temperatures exceeding 165 °C.