Advances in Hair Styling 420 agent. These essential components can be adjusted to obtain such properties as the correct viscosity, flow, and foaming. On top of the framework are added auxiliary ingredients that provide modifying effects essential to fine tuning the formula with respect to aesthetics, added benefits, and compliance to quality such as the use of preservatives. The main type of ingredient added to many of these vehicles for styling is the fixative resin. Here a polymer, usually high molecular weight and water-soluble, dries into a resinous film that imparts to the hair fibers or better still, fiber assemblies, the desired mechanical property of stiffness and elasticity. The chemistry of these polymers has evolved over the past 50–60 years. New monomer combinations with various functional groups have been added to increase the features and ultimately the benefits that these polymers can impart to the product as well as the hair style. Another formulation strategy is to modify the film qualities of a resin with auxiliary ingredients such as plasticizers. The addition of a polyhydric alcohol such as glycerin or an ethoxylated nonionic surfactant or emollient such as PEG 75 lanolin will tend to soften the film on the hair. This is due to the disruption of the interactive forces of the polymer molecules in the resinous film increasing film pliability. The result is to reduce flaking during combing, a problem with some of the homopolymers such as PVP, and improve smoothness properties. Negatives may be a compromise of other fixative properties, such as hold under humid conditions and reduced stiffness. This is the case with most cream gels that have a certain amount of oil, whether it is organic, petroleum-, or silicone- based oil, dispersed in the gellant. These gels compromise fixative properties such as stiffness for other benefits such as anti-frizz effects which require the addition of silicone. Examples of commonly used silicones include both low and high molecular weight dimethicone and dimethiconol, and phenyltrimethicone. A typical cream gel designed for normal and undamaged hair contains a small oil phase so that the oil does not weigh the hair down and create a negative