Chapter 13 417 influence on the durability of hair style. Hair shape (or shape of hair cross-section) also influences the ease of styling. Spherical shaped hair is harder to style (and to maintain the style) than elliptical shaped hair. The reader is advised to bear in mind this book’s other chapters which focus specficially on hair morphology, hair ethnicity, and the mechanical properties of hair. Hair Styling Products There are myriad and occasionally bewildering forms that styling products can take. Before getting into any detail on a given one, it will be beneficial to first take a broad look by describing the different categories of styling products, so that when a particular product is inspected we can automatically assign it to an aforementioned category. The first level of differentiation is whether a given product is put on the hair as a thickened liquid or a spray. With aerosols, the product is either atomized mechanically with the use of specialized pumps or with the use of pressurized and liquefied propellant gases such as propane. Variation increases dramatically for those products that are not considered aerosols. The spectrum of these products consists of clear to translucent gels, cream gels, low viscosity lotions, and pomades. The complexity of this range of product forms increases when we consider what has recently been termed “novel textured stylers.” These products have unique characteristics that are made possible through the creativity and expertise of the formulator. Examples in the market are taffies, stringing pomades, light-airy soufflés, clays, and waxes, to name a few. There are some cases where there is overlap between aerosol technology and those products that do not require atomization. For example, aerosol mousses dispense the product as foam but rely on a propellant as part of the delivery mechanism. There are also mousse products that produce their foam mechanically with the use of a special actuator. Spray gels require mechanical breakup as a non-aerosol, but the product form in the container is a gel.