AbstractA comparison between the viscosity‐molecular weight relationships for natural rubber degraded in thin films at 130 and 140°C. and on cold and hot mastication indicates a greater similarity of distribution on degradation by the mastication treatments. The hot mastication process is further differentiated from ordinary thermal reactions by the dependence of rate of degradation on the rate of shear. It does, however, differ from cold mastication in being primarily an oxidative‐scission reaction. No differences were detected in the properties of networks prepared from rubbers masticated at high or low temperatures to the same level of degradation.