What is a Durometer?
A durometer is an instrument for testing the hardness of various plastics & rubber. ASTM D2240 Standard Test Method for Rubber Property, Durometer Hardness. This test method covers twelve types of rubber hardness measurement devices known as durometers: Types A, B, C, D, DO, E, O, OO, OOO.
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.
ASTM D2240 durometers allow for a measurement of the initial hardness, or the indentation hardness after a given period of time. The basic test requires applying the force in a consistent manner, without shock, and measuring the hardness (depth of the indentation). If a timed hardness is desired, force is applied for the required time and then read. The material under test should be a minimum of 6.4 mm (.25 inch) thick.
Video: How to use a Durometer
Shore Hardness Chart for Polyurethanes