Hardness may be defined as a materials resistance to permanent indentation.

　　The hardness of rubber compounds is measured by the Shore Durometer.

　　Developed by Albert F. Shore in the 1920s, the term Durometer is often used to refer to the measurement as well as the device used to make the measurements.

　　The hardness of an elastomer is measured by creating an indentation on the material using a standard size and shape impact gauge. By comparing the difference between a small initial force and a much larger final a hardness figure can be given.

　　The International Rubber Hardness Degree (IRHD) scale has a range of 0 to 100.

　　The basic rule is that the higher the number, the harder the compound.

　　Softer compounds will seal better on rough surfaces, whereas harder compounds give better extrusion and abrasion resistance.

　　The surface indentation or hardness usually does not bear any relation to the ability of an elastomer part to function properly. Hardness is a measure of an elastomers response to a small surface stress.

　　Test methods:

　　ISO 48(IRHD)

　　ISO 7619 (Shore A)

　　ASTM D1415 (IRHD), D2240 (Shore)