In this diploma thesis the possibility to describe "viscous elastic" properties of plastics on the basis of two theories is examined. These theories are the Phan-Thien-Tanner-Theory and the Giesekus-Theory and are both implemented in the simulation program Polyflow. The finite element calculations for simple nozzle cross sections were done with the help of material data of a characterized polyethylene at the Institute of Plastics Processing in Leoben. Before calculating the models implemented in Polyflow the geometry determination, estimation of hardware requirements and simulation time had to be examined. Simple extrusion nozzles with different variations of the geometry were calculated in 2D and 3D and the received die swelling results were compared and discussed. The calculations showed an exact description of the flow ratio inside the nozzle and the subsequent area after the nozzle outlet. The PTT-Theory showed a better convergence behaviour in comparison to the Giesekus-Theory.