The extensional viscosity can be calculated with measured data of a capillary rheometer from the determined inlet pressure loss. In processing of plastics, the extensional viscosity occurs e.g. during fibre spinning, film blowing or foaming. The following diagram shows the typical course of shear and extensional viscosity. The increase in extensional viscosity is caused in this example by branching of the sample. To calculate the pressure loss in cross-sectional transitions, the extensional viscosity function is also used.