Chapter 10 339 In adsorption science, it is well recognized that the amount of a volatile species adsorbing on to a substrate is related to the relative vapor pressure, not the absolute vapor pressure.7 Figure 5 shows this same adsorption data now plotted against the absolute humidity of the environment, and demonstrates how only minor adsorption changes are obtained despite very large differences in the absolute water content of the atmosphere. The lower moisture content associated with elevated temperature relates to the more energetic nature of the gaseous molecules, which subsequently have diminished tendency for adsorption. Similarly, conventional daily use cosmetic treatments are recognized to have little influence on the shape of the hair-water adsorption isotherm.5 That said, our own studies contradict some findings from this earlier study concerning the effect of certain “chemical treatments,” where we often observe increased moisture content at elevated humidity (see Figure 6). Bleaching and waving Figure 4. Water adsorption by wool as function of relative vapor pressure and temperature