This document specifies the principles and procedures for estimating the thermal endurance of rubbers from the results of exposure to elevated temperatures for long periods. Two approaches are specified (see Introduction): — one using the Arrhenius equation; — the other using the WLF equation. In this document, the estimation of thermal endurance is based solely on the change in selected properties resulting from periods of exposure to elevated temperatures. The various properties of rubbers change at different rates on thermal ageing, hence comparison between different rubbers can only be made using the same properties.