Biaxial and uniaxial stress relaxation data are used to show that dimethyl siloxane rubber containing 28 wt.‐%SiO2as filler, exhibits, in the presence of large deformation, material behavior which is “viscoelastic” in the sense that it can be described, accurately, by the rheological equations of finite linear viscoelasticity. In particular, a constitutive equation for this material is found which containsthreerelaxation functions all of which are (a) proportional to the same function of time and are (b) independent of the deformation.