Trying to describe the relative tactility and hardness of an elastomer is difficult without a sample reference. The table below offers a level of guidance and comparison between scales. Rubber hardness is measured by comparing the difference in depth of indentation between the small initial force and the much larger final force applied by a standard size and shape impacting gauge. ISO International Rubber Hardness Degrees or IRHD uses a dead load to indent a rigid ball into rubber specimens, expressing the results in the range ‘0’ (corresponding to zero elastic or Youngs’s modulus) to ‘100’ (effectively infinite elastic modulus). Shore measures the material's resistance to a spring-loaded blunt point impressed on the surface. The primary difference between the two main Shore durability scales is that Shore A uses a truncated 35degree conical probe and Shore D uses a 30degree conical needle point probe.
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