The hardness of polymeric materials such as rubbers and plastics are usually measured in shore A or D scales.
Shore hardness of a material is the measure of resistance of the material to the penetration of a spring-loaded needle like an indenter on a device called a Durometer.
The measuring device and the actual hardness of the material are both referred to as the Durometer
Shore A scale is commonly used for testing soft elastomers (rubbers and most polymers), while the D scale is usually used to measure some hard polymers, hard elastomers and most other thermoplastic and thermoset materials.
The measured hardness is determined by the penetration depth of the indenter under load.
The shore hardness value may vary in range from 0 to 100 were the maximum penetration for each scale into the material is between 2.5 to 7mm deep This reading corresponds to a minimum shore hardness value of 0 while the maximum hardness reading of 100 corresponds to (0) zero penetration. It is recommend that ¼” (6.35mm) to 7mm thick test samples will give the best results. Whatever thickness you select always use the same and always use the same base to measure on so all your test results are constant.