Sulphur hexafluoride. A flourinated greenhouse gas (see also HFC and PFC). SF6 is used by industries in processing of magnesium and manufacturing of semiconductors, and as a tracer gas for detecting leaks. SF6 is also used in electrical transmission equipment, including circuit breakers, as insulation. The global warming potential (GWP) of SF6 is very high, making it the most powerful GHG that the IPCC has evaluated. Like PFCs, the effects of SF6 to date are relatively small. But due to their high persistance (i.e. long atmospheric lifetime) and GWP, SF6 has been banned or controlled for several uses in Europe.
Wikipedia.org (Sulfur hexafluoride)