Isobutane, also known as i-butane, 2-methylpropane, or methylpropane, is a chemical compound with the molecular formula HC(CH3)3. It is an isomer of butane and is a colorless, odorless gas. Isobutane is used as a precursor molecule in the petrochemical industry, for example, in the synthesis of isooctane. It is obtained by isomerization of butane. Isobutane is the principal feedstock in alkylation units of refineries, and using it, gasoline-grade "blendstocks" are generated with high branching for good combustion characteristics. Typical products created with isobutane are 2,4-dimethylpentane and especially 2,2,4-trimethylpentane. Isobutane is also used as a propellant for aerosol spray cans, and it is used as part of blended fuels, especially common in fuel canisters used for camping. It is also used as a refrigerant, fuel, and aerosol propellant, and in rubber. The FDA has reviewed the safety data associated with isobutane and has listed it as generally recognized as safe (GRAS), approving it as an indirect food additive and for use in the manufacture of foamed plastics. The Cosmetic Ingredient Review (CIR) evaluated scientific data and concluded that isobutane was safe as a cosmetic ingredient, confirming their conclusion most recently in 2002.