Hardness is the resistance of a body to penetration by a harder body of a specific shape at a specific pressure over a specific time.It is measured in Shore or IRHD (International Rubber Hardness Degree). Comparable values are determined using standard samples and given in Shore A units. For measurements on values of finished products deviate from those
of standard samples as their thickness, curved surface or values measured at the edges are not comparable and the metrology procedures differ.Measuring hardness at a cross-section ≤ 3mm is only feasible in IRHD.
Hardness must be adjusted to e. g. pressure load. The softer the elastomer the easier it is deformed under pressure and pressed into the gap to be sealed. On the other side softer elastomer seals at low pressures and between uneven surfaces due to its greater flexibility