788 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the number of fibers in contact with the comb. If one assumes the same total volume of fiber assembly is combed in each stroke, then the larger the individual fiber's volume, the fewer fibers in contact with the comb surface. Therefore an increase in fiber diameter should produce a small positive increase in combing ease. Measurement of primary properties at or near the same humidity for combing evaluations is necessary. With this in mind, (eq 3-5) hold for both wet and dry combing. Wet combing is a relatively well defined condition, while dry combing can involve any condition from zero to near 100% R.H. For wet combing, E and AE approach zero and can be neglected in (eq 4 and 5). This suggests that for wet combing, where there is no change in the hair fiber curvature, F k and F s are the important factors, since S and D play less important roles in both wet and dry combing. At low humidities, static charge becomes relatively important to combing ease. As the humidity is increased, the moisture content of hair also increases and its ability to acquire an electric charge decreases, i.e., AE decreases, rapidly becoming of less importance. At high RH, swelling of the fibers becomes greater, (AD increases) the fibers become less stiff and friction increases. Although AE approaches zero at high humidities and AD increases, making hair easier to comb, the other three factors Fs, Fk and S predominate making hair more difficult to comb. FLYAWAY Flyaway is the condition, during combing, in which hair fibers of an assembly separate due to repulsive forces of electric charge. We can consider two steps in flyaway: those factors which lead to charge build-up on the hair and the flyaway state itself. Those factors which lead to charge build-up during combing are those that increase the work of combing, which are described in the previous section by the combing ease equation 4, and the inherent ability of the fibers to acquire a charge. The flyaway state itself is influenced by five primary single fiber properties, see eq 6 and Table II. Flyaway = f(E, F•, S, C, W) (6) For hair products such as shampoos, hair sprays, creme rinses, groomers, etc., in which the active ingredients do not affect the hair fiber curvature and the hair styling is not changed as a part of the treatment, Aflyaway may be defined by (eq 7), illustrated schematically in Figure 2b. &Flyaway = + N1AE -- nlAF• -- n2AW -- n3AS (7) As suggested earlier, measurement of these primary properties is necessary at or near the humidity at which the flyaway is observed. Where there is no change in the hair fiber curvature, and at low humidities, flyaway is influenced principally by changes in E, (eq 7), and the greater the charge build-up on the fibers, the greater the flyaway. Opposing the extent to which the fibers may separate (flyaway) under a given electric charge, are S, W and F,. This latter term is considered to include the cohesive forces that exist between the fibers.

HAIR ASSEMBLY CHARACTERISTICS 789 As ambient conditions change and the humidity increases, the moisture content and AW increase and the fibers' ability to acquire an electric charge decreases, i.e., AE and flyaway decrease rapidly. The greater the fiber curvature, the greater the chance for fiber entanglements as the fibers separate due to electrical forces. Therefore the greater the fiber curvature, the less flyaway. Hair fiber curvature also plays a key role in the preflyaway condition, while the fibers are becoming charged. The greater the fiber curvature, the greater is the work of combing--one key factor which promotes the electric charge build-up on the fibers. Since the charging effect is opposite to that which exists at the charged state, it may "appear" as if hair fiber curvature enhances flyaway. Similarly, kinetic friction involved in combing or brushing of the fiber assembly influences the work of combing which in turn influences the amount of charge build-up and ultimately the extent of flyaway. BODY Body is defined in the textile trade as the compact, soft or firm feel of textile stock or fabric (2), a tactile property. In our beauty salon body is evaluated as apparent thickness or volume of the assembly, involving sight and touch for assessment. Both descriptions are consistent with the quality of liveliness or springiness (3) that is often associated with body. Our beauty salon generally evaluates body immediately after setting and drying, but evaluation over longer time periods is also relevant. An "increase in body" is not necessarily an improvement in hair behavior: hair with too much body may be unmanageable the stylist should be able to make the hair appear thick only where she wants it to appear thick. Also hair can have body and yet have poor style retention, e.g. the hair may not hold a style well, yet will appear thick in the relaxed Equation 8 states that six primary single fiber properties measured under the conditions for evaluation of body, describe this parameter for an assembly of hair. Body • f(Fs, Fk, S, C, D, W) (8) For those shampoos and creme rinses which do not generally affect the fiber curvature, body may be described by (eq 9). This equation appears in schematic form in Figure 2. &Body = + NIAF s -'}- N2AF k + N3AS + N4AD -- nlAW (9) An assumption inherent in this equation is that the hair styling is unchanged to the extent that fiber contacts are unchanged. In fact, for maximum body, fiber contact should be at a minimum. In effect, (eq 9) suggests that an increase in body will result by simply making the total hair assembly stiffer. This suggests that limpness is not enough body produced by making the entire fiber assembly less stiff, i.e., +ABody = --ALimpness. An increase in body according to (eq 9) is not time dependent and is consistent with our beauty salon evaluation. For treatments such as permanent waves, whose active ingredients affect the hair fiber curvature, increasing fiber curvature should increase body.