The Shore® Instrument Company has developed a wide range of instruments for the testing of the hardness of rubber, plastic, thermal plastics (TPE), and rigid plastics. These instruments are used in every industry to measure the materials that make up tires, golf balls, footwear, printer rollers, as well as industrial rubber and plastic products. They conform to all ASTM and international standards for measuring hardness, such as ASTM D 2240, DIN 53 505, ISO 7619 Part 1, and JIS K 6253.
The instrument, known as the durometer (pictured left), has an indenter with an accurately calibrated spring. When fully extended in the relaxed position the durometer gage is at zero (0). Hardness value is determined by pressing the gage onto a sample of defined thickness. The penetration of the indenter and spring move the gage from zero upward based on the amount of penetration. The lower the number, the softer the material. The highest value is always 100.
Durometer is normally allowed a tolerance of +/-5. That is, if a compound is said to be 40 durometer on the Shore A scale, then any tested batch could be between 35 and 45 durometer and still be acceptable as 40 durometer. Tighter durometer tolerances can be held when required.
There are a variety of durometer scales since elastomeric and plastic resins vary over a wider range than one scale can accommodate. Durometer is measured on a scale of Shore hardness. The different Shore types listed below dictate the shape and size of the indenter that is pressed into the material to determine the hardness. Shore type is chosen by the material classification and general hardness of the material.
- Shore A – Industrial rubber products and compounds
- Shore D – Hard plastics and for some very hard rubber compounds
- The Shore 00 – Sponge rubber and plastic foams
Use the form on the right to download our durometer chart to show you how these three scales overlap.
It’s also not uncommon for durometer hardness to be inaccurately confused with a few other physical properties of rubber, plastic, and foam materials. Click here to learn more about these common misconceptions.