This part of ISO XXXXX establishes a system of designation for polystyrene thermoplastic material, which may be used as the basis for specifications. The types of polystyrene plastics are differentiated from each other by a classification system based on appropriate levels of the designatory properties a) Vicat softening temperature and b) Melt mass-flow rate and on information about the intended application and/or method of processing, important properties, additives and colorants, fillers and reinforcing materials. This part of ISO XXXX is applicable to all amorphous polystyrene homopolymers. It applies to materials ready for normal use, unmodified or modified by colorants, additives, fillers, etc. This part of ISO XXXX does not apply to expanded polystyrene, styrene copolymers, homopolymers of substituted styrene or those modified with other polymers such as elastomers. It is not intended to imply that materials having the same designation give necessarily the same performance. This part of ISO XXXX does not provide engineering data, performance data or data on processing conditions which might be required to specify a material for a particular application and/or method of processing. If such additional properties are required, they shall be determined in accordance with the test methods specified in Part 2 of this International Standard, if suitable. In order to specify a thermoplastic material for a particular application or to ensure reproducible processing, additional requirements may be given in data block 5 (see 4.1).