Hardness of Foam

The instrument we use to measure “hardness” in our foams is an Asker Hardness Tester, Type ‘C’ (JIS ‘C’). This durometer has a ball-bearing probe that is pressed against the foam, it’s more suitable for measuring foams than the traditional Shore ’A’ hardness gauge, which is used predominantly in the rubber industry. The Shore ‘A’ gauge uses a sprung-loaded pin, which has the tendency to puncture the foam, thereby giving a false reading. The ball-bearing of the JIS ‘C’ gauge spreads the load and allows deflection without puncturing the foam.

Hardness Conversion Guide

*Hardness is read after pressing with the durometer for 2 seconds.

Jis C	45	50	55	60	65	70	75
Shore A	26.7	30.8	35.0	39.2	43.3	47.5	51.7

Temperature

Because temperature has an effect on hardness, these figures are standardised at 20 degrees Celsius.

For a hardness measured at temperatures other than the standard 20 degrees, an approximate guide is that for a decrease of 1.5 degrees Celsius, the hardness will increase by 1 degree JIS C.

Other

Hardness and density are not necessarily related. It is possible to compare two foams of the same density, but because they have different resin bases, or are made using different manufacturing methods, the hardness may be different. An example of this is our PE120, which has a hardness range of 55-65 JIS C, compared to our EVA120, which has a lesser hardness of 40-50 JIS C. As a general rule however, for the same group of foams produced under the same manufacturing method, as the density increases, so does the hardness.