The EPDM, Ethylene Propylene sponge is sulphur cured., TECHNICAL PROPERTIES:. . Hardness (solid) ASTM D2240 60 Shore A. Specific Gravity (Solid) BS ISO 2781:2008 1.18 g/cm3. Specific Gravity (Sponge) BS ISO 2781:2008 0.61 g/cm3. Mooney Viscosity (ML 1+4 @