1.1 This part of ISO 1622 establishes a system of designation for polystyrene thermoplastic material, which may be used as the basis for specifications1.2 The types of polystyrene plastics are differentiated from each other by a classificationsystem based on appropriate levels of the designatory propertiesa) Vicat softening temperature andb) melt volume-fow rateand on information about the intended application and/or method of processing, important properties, additives and colorants.1.3 This part of ISO 1622 is applicable to all amorphous polystyrene homopolymers.It applies to materials ready for normal use, unmodifed or modifed by colorants, additives, fllers, etc.This part of ISO 1622 does not apply to expanded polystyrene, styrene copolymers, homopolymers of substituted styrene or those modifed with other polymers such as elastomers.1.4 It is not intended to imply that materials having the same designation give necessarily the same performance. This part of ISO 1622 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 specifed in Part 2 of this International Standard, if suitable.1.5 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 3.1).