Adsorption Properties of Hair 334 inclement conditions. Alternatively, drier weather leads to a slight contraction in length and enticement for the diminutive fraulein to experience the glorious outdoor conditions. The purpose of this preamble is to emphasize that it has long been known that the properties of hair change in a significant and reproducible manner as a function of the relative humidity of the environment. Indeed, such is the magnitude of this dependence that experimental results on dry hair are of little use, unless the relative humidity has been controlled, recorded, and reported. With no background in hair, or indeed science, it is still easy to conclude that considerable differences are present in the properties of wet and dry hair. Single fibers of wet hair are distinctly more pliable: they are easier to stretch, require less force to break, yet can be elongated to higher extensions before failure. Similarly, running fingers over the fiber surface reveals that wet hair feels distinctly rougher. Personal experience has taught us that it is considerably more difficult to comb or detangle wet hair. Meanwhile, many will be familiar with the virtual impossibility of maintaining a hair style on hot, humid summer days, and have perhaps supposed a connection to the moist atmospheric conditions. Conversely, a similar dependence may have been conceived between the lack of moisture in the environment on cold winter days and a buildup of static flyaway during grooming. These simple observations indicate that water has a substantial effect on the properties of hair. The same observations have, of course, also been noted by inquiring scientific minds and over the years these areas have been probed and investigated with ever more sophisticated experimentation. Indeed, studies that quantified the manner by which fiber properties changed as a function of water content played a significant role in elucidating the complex structure of hair.1 Consequently, it is recognized that hair is able to absorb considerable quantities of water, which, perhaps most significantly, leads to swelling of fibers and a plasticization of the structure. As this swelling occurs, the outer protective cuticle scales are not held as tightly to the hair shaft, and, together with an overall increase in