If you want to show that your hair product, or hair styling device, prevents hair damage or restores its properties after being damaged, it is useful to perform a single-fiber tensile experiment.

In these studies, hair fibers are extended until they break.  The forces required to stretch and break the hair are good indicators of internal hair properties and overall hair strength.  Nearly all damaging treatments (bleaching, UV-light, heat styling etc) affect hair mechanical properties, so tensile experiments are usually the first test we would recommend for hair damage measurements.  These experiments can be used to investigate both hair damage prevention and the restoration of hair properties after being damage.

Hair fiber mechanical properties are very sensitive to the water content of the hair, and hence the humidity of the air.  Hair is much easier to break when it is wet.  Tensile experiments can be performed in both wet and dry conditions.  TRI can provide advice to you about which test protocol is most appropriate for your experiment.  It is widely believed that wet hair experiments focus most on the properties of the intermediate filament proteins (keratins) in the cortex.  Dry hair experiments investigate the combined properties of the intermediate filament proteins and the keratin associated proteins in the matrix.

TRI Publications
Evans (2013)