Chapter 13 429 type sprays. Hydrofluorocarbon 152a is very commonly used in aerosol hair care products and is often used to offset or eliminate the addition of water altogether however, due to its GWP (140 times that of CO 2 ), is often bypassed in the EU. Typical solvents employed in hair care products are water and ethanol, the latter of which is considered a VOC. Other solvents delivering enhanced functionality or finding application in more specialized products include methylal, isopropanol, aliphatic hydrocarbons, and as previously mentioned, methyl acetate and cyclopentasiloxane. The most significant ingredient employed in a hair styling product for delivering the desired performance is the styling polymer. There are many styling polymers offering a variety of on-hair benefits such as hold or humidity resistivity, and enhanced functionalities such as shine or conditioning. Choosing a polymer or a blend of polymers to deliver target attributes requires more than performance-based selection. The overall interaction within the finished system including such factors as compatibility with solvents, propellants, and packaging, and product delivery also must be considered. Product testing, packaging screening, and long-term stability protocols are necessary to ensure an acceptable product is achieved. The development of an aerosol system often presents the greatest challenge in satisfying these requirements, though other styling product forms also require attention. Aerosol systems, unlike other product forms, involve an additional component that is not represented in the solvent base– the propellant. Propellant use levels can be greater than 50 weight % of the finished formulation, therefore the product requires evaluation in its complete form not only in performance but in overall compatibility and deliverability. To take a product base that is stable and functional on its own and assume that simply adding a propellant will provide a suitable system ignores the interaction of the propellant and resultant final product. This also holds true for switching one propellant for another. Developing an aerosol