The smoothness of shaven beards: the relation between stubble length distribution and skin parameters and tactile smoothness.

In this report we describe how the tactile smoothness of shaven beards depends on the distribution of the stubble lengths remaining after shaving and on various skin parameters like coarseness and scaliness. To this end, we set up two experiments on perceived smoothness with blinded human judges. In the first experiment we used artificial beards with various stubble length distributions and stubble densities as stimuli. In the second experiment we presented freshly shaven human beards, for which a wide range of objective skin and stubble parameters had been measured, as stimuli. The results of the two experiments are mostly in line with each other. We can conclude that there are individual differences between judges in the aspects they pay attention to when judging tactile smoothness. Nevertheless, a general line is discernable, and we can identify three parameters that influence the impression of tactile smoothness: the orientation of the stubble, the density of the stubble, and the length of the hairs in the stubble length distribution. We have also established the relative importance of the latter two effects.