A durometer measures a material’s resistance to permanent indentation (one of several measures of hardness). It’s normally used to measure plastic and rubber, which have some resistance to permanent change. Durometers compare relative results only, and this quantity therefore has no units. A durometer uses one of many possible scales due to the wide range of hardness that flexible materials may have. The specific properties of the material being measured will determine the proper scale to use.
Select the proper durometer for the test material. There are 12 durometer scales, with the A and D scales being the most common. The A scale is for softer rubbers such as car tires and the D scale is for hard rubbers like bowling balls.
Examine the meaning of a durometer reading. A material that does not indent at all under a particular scale has a durometer reading of 100 on that scale. A material that allows the maximum indentation (2.5 mm on the A and D scale) has a durometer reading of 0.
Study the parameters for the durometer scale you intend to use. The A and D scales both require you to take the measurement at least 12 mm from the edge of the material and the required pressure must be applied for 15 seconds. Furthermore, the material must be at least 6.4 mm thick. If the material is thinner than this, you can use additional layers of the same material to achieve this minimum thickness.
Take the durometer reading using the specific parameters for the scale you’ll be using. Apply the spring-loaded foot of the durometer to the material with sufficient force to make the spring begin to compress. This force should be 0.822 kg for a type A durometer and 4.55 kg for a type D durometer.