This part of ISO 14910 establishes a system of designation for thermoplastic polyester/ester and polyether/ester elastomers, which may be used as the basis for specifications. The types of thermoplastic polyester/ester and polyether/ester elastomer are differentiated from each other by a classification system based on appropriate levels of the designatory properties a) hardness; b) melting temperature; c) tensile/flexural modulus of elasticity; and on information about the intended application and/or method of processing, important properties, additives, colour, fillers and reinforcing materials. This part of ISO 14910 is applicable to all thermoplastic polyester/ester and polyether/ester elastomers. It applies to materials ready for normal use in the form of powder, granules or pellets, unmodified or modified by colourants, fillers or other additives. It is not intended to imply that materials having the same designation give necessarily the same performance. This part of ISO 14910 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 ISO 14910-2, if suitable. In order to specify a thermoplastic polyester/ester or polyether/ester elastomer for a particular application or to ensure reproducible processing, additional requirements may be given in data block 5 (see 3.1 and 3.6).