Durometer is an international standard for measuring the hardness of material and can be determined using a Shore Hardness Scale and a Durometer Hardness Test.

The hardness of material is an important property that helps determine the suitability of a rubber product for its intended use. Additionally, a components’ application is critical to determining the necessary hardness. For instance, softer compounds that offer less resistance are fine for low-pressure seals where the material must conform to rough or uneven surfaces. Harder materials would be more appropriate for high-pressure seals.

Shore Hardness Scales measures the hardness of different materials. These scales establish a common point of reference for comparing materials, with durometer being bucketed into three Shore categories on a hardness scale from 0 to 100:

  • 00 – Measures light foams, sponge rubber and gels that are very soft
  • A – Measures soft rubber, plastics, and rubber-like elastomers
  • D – Measures hard rubber, plastics, and thermoplastics

The image below shows examples of different materials and what Shore hardness category they fall into. Note: It is possible for materials to fall into more than one category.

Shore Hardness Scale: Shore 00, Shore A, Shore D

In the case of rubber, a durometer is also defined by its relative resistance, or its ability to deflect the depth of indentation made by an indenter. The illustration below shows the difference between a Shore A material and a Shore D material.

Durometer hardness test, applied load vs durometer indenters

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