Polymers are extensively used in engineering applications, ranging from sealing rings to dampers and springs in centrifugal separators as well as in micro robots with piezoelectric excitation. The mechanical behaviour of these materials is highly non-linear and may be described by integral equations, taking into account the load history of the part considered. Paper shows taht long-term deformation in creep and relaxation can be derived from tensile tests at several loading rates. The influence of cyclic loading is discussed. Tests show that material can fail in fatigue.