1.1 This International Standard specifies two methods for the determination of the thermal stability of products and compounds based on vinyl chloride homopolymers and copolymers (referred to simply as PVC in the following text) by the extent of the discoloration that occurs when they are exposed, in the form of sheet, to elevated temperatures. — Method A: Oil-bath method — Method B: Oven method 1.2 These methods are particularly applicable to the determination of the resistance of PVC to degradation by heat, as assessed by the change in colour after different times of heating under standardized conditions. The results are comparative only, and may be unsatisfactory when coloured PVC materials are tested. 1.3 Method A is a simple method, which requires little expenditure on apparatus and permits materials to be tested almost in the absence of air. Method B requires a forced-air oven, in which the air flow is adjusted to provide a sufficiently uniform temperature throughout the entire test area. This method is not applicable to materials that will cross-contaminate during oven exposure. The stability times given by the two methods may not be similar and cannot be used for direct-comparison purposes.