Chapter 15 511 re-adsorption of water however, as discussed in Chapter 10, this supposition is difficult to prove, and water is a difficult molecule to deter. Nonetheless, consumer acceptance illustrates the efficacy of such products, which can also be demonstrated in the laboratory. Figure 11 shows frizzy Mulatto hair tresses suspended inside a bench- top humidity chamber. High quality photography coupled with image analysis approaches can be used to quantify the shape and volume of tresses. Baseline values are obtained for both initial and straightened states of the hair at low humidity, and subsequently, the relative humidity is raised to some elevated level with continued measurement of the tress shape over time (see Figure 12). Results do indeed show the ability for certain leave-in products to reduce reversion rates to varying degrees. That said, it appears likely that the additional weight imparted by surface deposits is a significant contributor to efficacy. While initially there may be debate about what goes into defining the consumer term “frizz,” the antithesis is probably easier to define. Namely, highly aligned, possibly even bone-straight hair clearly contains no frizziness. In this state, hair appears sleek and smooth, it is shiny, and possesses a fluid flowing motion, yet all these properties arise from the underlying fiber alignment. Heat styling or chemical treatments are frequently employed to reach this state in spite of their well-known damaging potential. It therefore appears reasonable to suggest that complaints relating to “frizz” involve an Figure 12. Progressive reversion of straightened hair upon exposure to elevated humidity