Understanding the Shore Durometer and Its Values

Invented in the 1920s by Albert F. Shore, a durometer is a specialized instrument that measures the hardness of a material based on its indentation strength resistance. Durometer measuring instruments vary in size, but many are hand-held. Pressed against the material being tested, whether it’s automotive foam or a plastic, it’s forced down until the spring-loaded pin tip is either pushed into the shaft, or the base of the shaft meets the surface of the test material. Depending on the hardness of the test material, the pin may get forced into the durometer, as happens with hard products like rubber, or indent the material, which is what happens with soft products like foam bed toppers.

There are various scales that measure these values because of the different kinds of materials Durometers test, from hard plastics, to soft foams. The three most popular Durometer scales are “A,” a median scale spanning the widest range of materials, “D,” for the hardest plastics, and “OO,” for soft materials like cushions or foam firm enough for packing. On all scale types, measurement values are placed on a scale from zero to 100, with 100 being the hardest possible value, and zero being the softest.

Real-life values can be better comprehended from Shore Durometer hardness testing, in particular pressure resistance and a material’s flexibility. It’s important to note that with certain materials, the thickness and weight supported will impact resistance to pressure and flexibility differently than a small sample tested under a small spring-loaded pin. For that reason, a durometer rating should be used as a starting point in understanding the performance material, but is useful to have in your knowledge set.