Hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) are synthetic chemicals that are used in a variety of industrial production processes such as semiconductor manufacturing. PFCs are also produced as a by-product of aluminum smelting. Both groups of chemicals are finding increasing use as substitutes for ozone-depleting chlorofluorocarbons (CFCs), which are being phased out under the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. HFCs and PFCs are replacing CFCs in applications such as refrigeration and foam-blowing for insulation.