This part of ISO 19063 establishes a system of designation for impact-resistant polystyrene (PS-I) moulding and extrusion materials, which may be used as the basis for specifications.The types of impact-resistant polystyrene plastic are differentiated from each other by a classification system based on appropriate levels of the designatory properties:a) Vicat softening temperature;b) melt mass-flow rate;c) Charpy notched impact strength;d) flexural modulus;and on information about composition, intended application and/or method of processing, important properties, additives, colorants, fillers, and reinforcing materials.This part of ISO 19063 is applicable to all impact-resistant polystyrene plastics with a two-phase polymer system comprised of a continuous phase, consisting of polystyrene and/or a copolymer of styrene with an alkyl-substituted styrene, and a dispersed elastomeric phase based on butadiene.It applies to materials ready for normal use, unmodified or modified by colorants, additives, fillers, etc.