The property of hardness is easily recognised, but in design it must be specified to achieve a given objective.
Solid rubbers range from 20° to 98° Shore A, where 20° is extremely soft like foam and 98° is as hard as bakelite or nylon. As a reference, the ball of the human thumb is 25°, a Staedtler white rubber eraser 55° and a bath plug 95° Shore A.

Typical Applications

Designers use rubber in its whole range of hardnesses and each application has to be individually considered. Once a mould has been produced, it is relatively easy to make the same part in other colours and hardnesses to suit different functions.

Whatever the hardness required, it may still be necessary for a rubber component to deform in order to seal against an uneven surface or to resist abrasion.