The results of psycho-physical scaling experiments have shown that a property such as softness can easily be scaled like other subjective variables such as loudness and brightness. They have also shown that bulk softness and surface softness should be treated separately.
In search for physical measurements correlating with the subjective properties, one has to proceed along slightly different pathways. For bulk softness, a known physical property-bending stiffness (or, more correctly, inverse bending stiffness)- has been chosen as a good substitute for subjective bulk softness.
An instrument using a ‘synthetic fingertip’ has been developed for measuring surface softness. The basic principles of the system, as well as recent experimental results are reported.