Experimental data on the heat generated during torsional oscillations of polymethylmethacrylate tubes are presented. Various factors which affect the internal heat generation, including the amplitude and frequency of oscillation and the ambient temperature are investigated. A comparison of the mechanical energy added to a specimen during a cycle of deformation and the resulting heat indicates that some energy is ``stored'' during the process. In addition to the detail of the response during a single cycle of deformation, the longtime response of the material to constant strain‐amplitude oscillations is investigated. The data demonstrate that thermomechanical coupling effects can be extremely important.