Durometer, also known as Shore durometer, is a standardized way of measuring the hardness of materials like rubber and plastic. It is a measure of how resistant a material is to deformation caused by mechanical indentation or abrasion. Durometer measurement scales range from 0 to 100, but there is no such thing as a durometer unit of measurement. Durometer numbers simply represent a relative comparison of hardness between different but similar materials that have had their hardness measured using the same durometer scale, device, and measurement standard.

Durometer, like many other hardness tests, measures the depth of an indentation in the material created by a given force on a standardized presser foot. This depth is dependent on the hardness of the material, its viscoelastic properties, the shape of the presser foot, and the duration of the test. The ASTM D2240 standard recognizes twelve different durometer scales using combinations of specific spring forces and indentor configurations. These scales are properly referred to as durometer types, and each type is specifically designed to determine a specific scale.

In general, a higher durometer elastomer or plastic is harder than a lower durometer elastomer or plastic. For example, a 90A durometer polyurethane tubing is harder than a 70A polyurethane tubing. Durometers range in scales of 10 with acceptable tolerance of plus or minus 5 points. For example, a Shore 60A material will have a lower acceptable limit of 55A and a higher acceptable limit of 65A.

Durometer is an important measurement for engineers and product teams to consider when manufacturing with plastic or elastomer. Engineers can test a materials hardness using a durometer tester, which looks like a round tire pressure gauge and has a needle on a calibrated spring extending from one end. Once the needle has penetrated the material as much as it can, the measurement needle indicates the corresponding durometer hardness on the appropriate scale.

In summary, durometer is a dimensionless but standardized measurement used to indicate the hardness of a material. It is measured by the depth of an indentation into the material under a standardized force, and it ranges in scales of 10 with acceptable tolerance of plus or minus 5 points. Durometer numbers represent a relative comparison of hardness between different but similar materials that have had their hardness measured using the same durometer scale, device, and measurement standard.