In general, polymers show time-dependent stress-strain responses. The responses can be measured in a time-based test (e.g. a stress relaxation test) or a frequency-based test (e.g. a rheometer test). In a stress relaxation test, it is easy to measure the long-term stress (i.e. the low frequency response) accurately, but it is very difficult, if not impossible, to measure the short-term stress (i.e. the high frequency response) accurately. In contrast, in a rheometer test it is easy to measure the high frequency response by lowering the temperature around the specimen, but it is almost impossible to measure the low frequency response by increasing the temperature over a threshold. Thus, in this paper, a method to combine the two test results was proposed to model a polyurethane stopper for a wide range of frequencies. This method was proven to be valid by showing that simulation results for a drop test and a torque test were in good agreement with test data for a polyurethane stopper used in a robot.