Advances in Hair Styling 440 reduction in cohesion and the higher adhesion of the higher charged density polymer becomes more discernable. This is a good example of how the polymer’s adhesion to the hair, promoting fiber-fiber linkages, as along with the cohesive properties of the polymer film are important to consider in the polymer’s fixative properties. Evaluation Techniques During the course of the product development process, there are various test methods that are employed to substantiate efficacy. In the early stages, instrumental techniques are used to screen for aesthetics and performance. As the development process evolves and if toxicological assessment has been achieved, then evaluation can commence on human panelists. Salon and consumer use studies are time-consuming and expensive, therefore the product evaluation typically progresses from in vitro measurements and trained panel evaluation to help screen and develop the formulation against its project profile. Screening tests can include work on human hair tresses. Synthetic or human hair mannequin heads may be employed to determine full head or half-head styling benefits. For in vivo testing, reference is made to the project brief to determine the target market with respect to hair type/origin, degree of damage, and hair length, as well as key attributes/claims for example, 24 hour hold protects hair and enhances straightening, volumizing, etc. Styling products can be applied throughout different stages of the styling process, and it is important that performance evaluation reflect the consumer/styling application. Successful development of the styling product has been reached when the technical objectives have been met, claims statistically substantiated, and performance versus appropriate benchmarks is accepted by the consumer. When the consumer perceives the product as having the claimed benefit, market success of the product is greatly increased.36 Evaluation techniques used in the product development process are outlined in Figure 8. This section is meant to provide a cross-section of the typical test methods employed in each stage of the process without dwelling on details of test methodology.