Abstract The process of cold mastication has been rationalized in terms of recognized chemical reactions, and its essential difference from the hot mastication process has been demonstrated. Many apparently unrelated phenomena occurring on cold mastication, as, for example, are collected in a recent survey, can be interpreted as specific manifestations of the general scheme now presented. A clearer understanding of the basic function of the masticator is relevant to the design of such machines, i.e., the provision of high shearing forces for low-temperature chain rupture and the exposure of large surface area for high-temperature autoxidative breakdown. No acceleration of cold plasticization by added compounds is normally obtainable under the shear conditions of the Banbury mixer, but may be encountered under more efficient shear and in oxygen-deficient conditions. Cold mastication is revealed as a versatile method for producing rubbers of a wide variety of physical properties, i.e., softer (linear degraded) rubbers, harder and soluble (branched or cross-linked) rubbers, and insoluble (cross-linked) rubbers.