Some simple theoretical considerations on the bending stiffness of human hair

Synopsis Factors affecting the cantilever bending of human hair have been investigated by theoretical structural mechanics in which the hair was treated as if it was of isotropic structure and internal mechanical property. Despite the simplicity of the model it is a valuable one for assessing the major geometric factors affecting a hair's bending behaviour in relation to perceptions of coarseness and fineness. Simple equations have been used for predicting relative bending stiffness between hairs of different racial types using published fibre cross-sectional information and these accord with existing perceptions of behaviour. Strikingly it is the hair's minor elliptic diameter which has a dominant effect upon bending resistance and it is shown that the hair's cuticle could be making a very high proportional contribution. It is shown that triangular hairs of the uncombable hair syndrome will be stiffer than normal elliptical hairs of the same cross-sectional area and that this goes some way to explaining the condition.