This part of ISO 7792 establishes a system of designation for thermoplastic polyester (TP) material, which may be used as the basis for specifications. It covers polyester homopolymers for moulding and extrusion based on poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(cyclohexylenedimethylene terephthalate) (PCT), poly(ethylene naphthalate) (PEN), poly(butylene naphthalates) (PBN) and other TP-types and copolyesters of various compositions for moulding and extrusion. The types of thermoplastic polyester are differentiated from each other by a classification system based on appropriate levels of the designatory properties (viscosity number and tensile modulus of elasticity) and on information about the intended application and/or method of processing, important properties, additives, colorants, fillers and reinforcing materials. This part of ISO 7792 is applicable to thermoplastic polyester homopolymers and copolymers. It applies to materials ready for normal use in the form of powder, granules or pellets, unmodified or modified by colorants, additives, fillers, etc. This part of ISO 7792 does not apply to the saturated polyester/ester and polyether/ester thermoplastic elastomers covered by ISO 14910. It is not intended to imply that materials having the same designation give necessarily the same performance. This part of ISO 7792 does not provide engineering data, performance data or data on processing conditions which may 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 polyester material for a particular application or to ensure reproducible processing, additional requirements may be given in data block 5.