Finite element (FE) simulations of how rubber materials for seals behave over time isperformed. The application is seals for nuclear power plants where seals are exposed toelevated levels of ionizing radiation and temperature.A major challenge for the simulations is to find an appropriate material model for the rubbermaterials and how to calibrate it to experiments. Here is a material model proposed that caninclude effects like creep, permanent set, and temperature dependence. Calibration of materialmodels for relaxation tests on EPDM rubber is performed and presented with good results.Further modelling to include more effects in the material and to simulate leak and tightness ofseals are proposed.