The IRHD Hardness Tester is used to determine the indentation resistance of elastomeric and rubber materials by measuring the depth of penetration of a spherical ball indenter under a specified load. It is widely used in rubber and polymer testing laboratories for accurate hardness evaluation.

In this method, an initial contact force is applied to the indenter and the penetration is set to zero. The force is then increased to a specified total load, and the resulting depth of penetration is measured. The IRHD value is directly related to the depth of indenter penetration — the smaller the penetration, the higher the hardness value.

For highly elastic materials, IRHD values are generally comparable to Shore A hardness values. An IRHD value of 0 indicates a material with zero Young’s Modulus, while an IRHD value of 100 represents a material with an infinite Young’s Modulus.