Hardness scales for TPE and rubber elements

Thermoplastic elastomers (TPEs), or thermoplastic rubber compounds as they are sometimes called, are a class of materials that behave like rubber but can be processed like plastic. TPEs consist of hard and soft phase mixtures in the form of mixtures, alloys or polymers. TPE materials are often used in situations that require a soft touch, such as gripping the toothbrush handle, or when flexibility is desired. TPEs can even be used to absorb energy in acoustic or vibration damping solutions. TPEs are quite unique materials because, depending on the recipe, they can be in the form of an ultra-soft gel or a hard plastic, e.g. polypropylene. Thus, "Hardness" is an important property that is measured and specified for TPEs.

Hardness is measured in Shores. Hardness scales were created to provide a common reference point for comparing different materials. The Shore hardness is measured with a durometer using a spring-loaded steel bar which is pressed against the surface of the TPE. The reading 0 Shore describes the maximum possible sinking of the rod and 100 Shore shows that the sinking is almost non-existent or the material has very strong resistance to it.

There are different Shore hardness scales for measuring the hardness of different materials. For each scale, there is a different shape of the sample rod or well and a specific spring force.

The Shore OO scale measures particularly soft materials such as gels (eg gel insoles).

The Shore A scale measures a variety of material types; from very soft and elastic to semi-hard plastic with almost no elasticity.

The Shore D scale measures very hard rubbers, semi-hard and had plastics (such as PVC pipe). Overlap on different scales. For example, a material with a Shore hardness of 95A is also a Shore 50D. TPEs can range from 10 Shore OO to 72 Shore D, covering all three hardness scales, but the Shore A scale is still the most commonly used.