Chapter 10 359 hence the prolonged soaking and elevated temperatures conditions used in this work. This may appear surprising as perhaps it may have been supposed that the ready penetration of liquid water into hair leads to the equally easy diffusion of dissolved species. However, this does not appear to be true, and an analogy may be drawn to liquid chromatography, where the mobile phase readily passes though a stationary phase while dissolved components progress at different rates depending on interaction energies. Nonetheless, an ability to manipulate the water content provides a means for tailoring the mechanical properties of hair. It is worth pausing to highlight the novelty of this idea. Conventional daily use hair care products are based on large molecules (e.g. surfactants, polymers, oils) whose functionality lies predominantly at the hair surface. Therefore, there may be a whole next generation of products still waiting to be discovered that act to modify the internal properties of hair. Figure 19. Adsorption and desorption isotherms for hair soaked in a 5% resorcinol solution relative to an untreated control