Understanding the Shore Durometer and Its Measurements
Invented in the 20s by Albert F. Shore, a durometer is a dedicated instrument that measures the hardness of a material based on its resistance to indentation strength. Durometer instruments vary in size, but many are hand-held mechanisms. Held against the material to be tested, whether it’s automotive foam or a plastic, it’s forced down until the spring-loaded pin tip is pushed into the shaft, or the base of the shaft is flush with the surface of the test material. Depending on how hard the material its, the pin may get forced into the durometer, as happens with hard products like rubber, or indent the material as happens with soft products like foam bed toppers.
There are various scales to measure values because of the different kinds of materials these instruments can test, from hard plastics, to soft foams. The three most popular scales are “A,” which is a median scale spanning the widest range of materials, “D,” for the hardest plastics, and “OO,” for the softest materials like cushions, extra firm foam, and rubber. On all scale types, measurement values are ranked from zero to 100, with 100 being the hardest possible value, and zero being the softest.
Real-life values can be better understood from Shore Durometer hardness testing, particularly pressure resistance and material flexibility. It’s important to note that with certain materials, thickness and weight supported will impact its resistance to pressure and flexibility differently than a sample and a small spring-loaded pin. That’s why a durometer rating should be used for a starting point in understanding the performance material, but is still important to have in your knowledge set. But understanding that a softer-rated material will resist pressure less and flex more can help narrow down product choices and make more educated purchase decisions.