This International Standard specifies the general principles of a method for determining the transient extensional viscosity of polymer melts. The procedure details the measurement of polymer melt specimens stretched uniaxially under conditions of constant strain rate and constant temperature. The method is capable of measuring the transient extensional viscosity of polymer melts at Hencky strain rates typically in the range 0,01 s–1 to 1 s–1, at Hencky strains up to approximately 4 and at temperatures up to approximately 250 °C (see Notes 1 and 2). It is suitable for measuring transient extensional viscosity values typically in the range from approximately 104 Pa·s to 107 Pa·s (see Note 3). NOTE 1 Hencky strains and strain rates are used (see Clause 3). NOTE 2 Values of strain, strain rate and temperature outside these limiting values may be attained. NOTE 3 The operating limit of an instrument, in terms of the lowest transient extensional viscosity values that can be measured, is due to a combination of factors, including the ability of the specimen to maintain its shape during testing and the resolution of the instrument. A list of documents related to this International Standard is given in the Bibliography.