Shore Hardness measures the resistance a material has to indentation. The hardness of a material is measured used a device called a durometer. The device measures the depth of an indentation created in the material created by a given force on a standardised presser foot. The result is rated on scale known as a Shore Hardness scale or Durometer scale. A higher number on the scale indicates greater resistance, so therefore a harder material. Softer material s are lower on the scale.
Whilst there are a several scales used for different materials, in engineering plastics, Shore A and Shore D are most commonly used.
The Shore A scale is usually used for softer, more flexible plastics, and the Shore D scale is predominantly used for harder materials