Abstract: Keratin fiber condition is evaluated by testing dry hair to determine analysis factors. For each factor, two values of elongation are determined by measuring the force required to obtain a first value and a second value of elongation of the fiber. The percent total elongation of the fiber to its break point is also determined. The ratio of the two measured forces is used with the percent total elongation in empirically derived nonlinear equations to determine analysis factors, such as a condition factor and a moisture factor. It is found that each factor is independent of fiber diameter or the source of the fiber. It is also found that the factors change as a function of subjective or objective measures of chemical damage to, and moisture content of, the hair fiber. The factors can, therefore, be used for identifying hair care products suitable for application to the hair without inducing unacceptable damage.