In the simulation of plastics processing, the quality of the material data is very important. The more precisely the material data is recorded, the better the simulation results correspond to the real processing conditions on the machine. For this reason, it is becoming increasingly important to be able to determine properties, such as viscosity, as closely as possible to the process. The aim of this thesis was to investigate the influence of the processing history of the injection molding process on the viscosity of a thermoplastic elastomer (TPE) and to show possible changes in simulation results. In the first step, the viscosity of the TPE was determined with a high-pressure capillary rheometer and an injection molding machine rheometer. In addition, these results were compared with each other. This first comparison showed that there was a difference in viscosity due to the measurement on an injection molding machine. Subsequently, multiple simulations based on two material data sets of the TPE were performed in Moldflow. The difference between the two material data sets were only in the viscosity at high shear rates. One set was made with viscosity measured with the high-pressure capillary rheometer, the second one with the injection molding machine rheometer. The other material data such as the specific heat capacity, thermal conductivity, density and the viscosity at low shear rates were incorporated in both data sets. Differences between the two measuring principles could already be determined from these first two questions. In order to show possible influences on simulations of injection molds, final tests were carried out on a mold with a cavity pressure sensor. Subsequently, several simulations were carried out on this tool. A comparison between the measured values from this experiment and the simulation also showed the influence of the selected viscosity measurement method.