790 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS MANAGEABILITY In cosmetic terms, manageability is concerned with the ease of arranging hair in place and its temporary ability to stay in place. This property is evaluated in our beauty salon immediately after setting and drying and is not concerned with longer term effects on the hair fiber assembly. Equation 10 states that six primary single fiber properties measured under the conditions for manageability evaluation determine this parameter (K manageability) for an assembly of hair, see Table I. For hair products Manageability • f(Fs, Fk, S, E, C, W) (10) such as those shampoos, hair sprays and creme rinses whose active ingredients do not affect the hair fiber curvature and for unaltered styling, change in manageability may be defined by (eq 11). This equation is illustrated in schematic form in Figure 2d. AManageability -- Nz/kF k + N2AFs -- n•AS -- N3/kE -- n2AW (11) Equation 11 suggests that manageability will be increased by decreasing Fk, E, S and W. Stiffer fibers are less flexible and are therefore less manageable. However fiber stiffness is less important than E and F k. The effects of humidity on static charge and flyaway have already been described and an increase in W may decrease the "staying in place" part of manageability to a small extent. The opposite signs in the two friction terms suggest that maximizing the force required to initiate movement between surfaces (to transiently hold style in place) and minimizing the force to maintain movement of surfaces past one another will increase manageability. A certain minimum amount of F k helps to maintain a harmonious assembly pattern in styling movements. If F k is high before treatment, then our friction analysis in manageability is almost certainly correct as F k approaches the minimum required value, however, modification to (eq 11) may be required. If the fiber curvature is altered in any way such as a change in set or the ability of the fibers to accept a water set, it will be reflected in the manageability of the hair, i.e., if the treatment changes the fiber curvature so that it is either too straight or too kinky, for the particular style desired, it will be less manageable. STYLE RETENTION Style retention may be defined as the capability of hair to stay in place after styling. Since style retention is time dependent, evaluation should involve a time period of several hours to a few days as compared to evaluation immediately after setting. Style retention includes curl or wave retention. Equation 12 states that five primary single fiber properties measured under the conditions for style retention evaluation, describe style retention for any assembly of hair fibers, see Table II. Style retention = f(Fs, Fk, S, C, W) (12) For hair products such as those 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, style retention may be defined as in (eq 13). See the

HAIR ASSEMBLY CHARACTERISTICS 791 schematic illustration of this equation in Figure 2e. Equation 13 suggests that style retention may be increased by increasing F s and Fk, with Fs being the more important factor. &Style retention = q- N•AF s -3- n•AF k -- n2AS -- n3AW (13) Increases in S and W can decrease style retention. The role of W is rather straightforward, while that of S is more subtle. Since style retention is time dependent as contrasted to the other assembly properties defined in this report, the natural changes that occur to hair fiber curvature--from immediately after water setting and styling until equilibrium is reached-- are of extreme importance. The fibers on a head are generally water set to produce a desired contour. Changes in humidity promote a deterioration of the water set and a change in the hair fiber curvature. Therefore hair fibers that have been water set, styled and exposed to ambient conditions do not have the same curvature stresses as after setting and styling. Frictional forces primarily tend to hold the assembly in the "set" style. Thus these natural curvature changes induced by water vapor absorption produce transient stresses within each fiber assembly. These stresses, which are dependent on the amount of curvature change and fiber stiffness, tend to decrease the style retention. In the hypothetical situation that assumes no changes in fiber curvature due to humidity, the maximum fiber curvature consistent with the desired hair styling will produce the maximum number of possible entanglements and therefore the maximum style reten- tion. For treatments such as permanent waves in which the active ingredients produce changes in the "relaxed" hair fiber curvature or for polymer depositions or graftings, which may also change the hygroscopicity of the hair, the rate and extent of change in hair fiber curvature in response to humidity is altered. METHODS FOR EVALUATING PHYSICAL PROPERTIES Both single fiber and fiber assembly methods are available for most of the properties described in this report. Single fiber methods have been described for friction (5), stiffness (6,7), static charge (8), and fiber diameter (3, 9, 10). Fiber curvature may be estimated from the fibers relaxed length and its taut length. Fiber assembly methods have been described for combing ease (11, 12), flyaway (13, 14, 15), body (3) and percentage of set retention (3). Manageability is the most complex of these assembly properties and a quantitative method for this property has not been described. CONCLUSIONS Changes in the behavior of hair assemblies can be usefully represented in algebraic form as combinations of changes in single fiber properties. Considering directional changes instead of absolute values leads to useful simplifications. A summary of how the assembly behaves as a function of changes in the single fiber properties follows. 1. Combing changes depend primarily on frictional effects (including cohesive forces), static charge and fiber curvature. For most products other than permanent waves and straighteners, changes in fiber curvature are negligible and for wet combing, static charge is not relevant.