Abstract The specific volume, compressibility, and volume thermal expansivity of rubber-sulfur compounds containing from 3 to 31 per cent of sulfur have been measured at pressures from 1 to 800 bars and at temperatures from 10° to 85° C. The results are expressed in tables, curves, and equations, so that within the indicated limits the value of any of the above properties can be readily determined for a compound of specified composition under specified conditions of temperature and pressure. Specific volume, which is the reciprocal of the density, has been used throughout this paper, because this term is the one which is used directly in the definitions of compressibility and volume thermal expansivity. The work of Kimura and Namikawa indicated that the specific volume of rubber-sulfur compounds at atmospheric pressure was a linear function of the temperature. The use of the specific volume thus leads to equations which are simpler than if the density is used.