The static modulus of rubber depends not only on the hardness, but also on the temperature used. For example, the elastic modulus of the rubber is lower, the higher the hardness, the lower the elastic modulus and the higher the temperature. In this case, the static modulus is three times the shear modulus, ie E = 3G0, and the relationship between the hardness of natural softwood and natural rubber can be calculated by the following equation.