This International Standard specifies a method for the determination of the resistance of moulded test specimens of polypropylene and propylene-copolymers to accelerated ageing by heat in the presence of air using a forced draught oven. The method represents an attempt to estimate the Service life of Parts fabricated from propylene plastics. The stability determined by this method is not directly related to the suitability of the material for use when different environmental conditions prevail. NOTE - The specified thermal levels are considered sufficiently severe to Cause failure of commercial grades of heat-stable propylene plastics within a reasonable period of time. If desired, lower temperatures tan be applied to estimate the performante of propylene plastics with lower heat stabilities.