Highly electronegative elements, e.g., halogens, are favored as they rapidly recombine with the ions present in the discharge channel.
Other compounds, which dissociate only in the discharge pathway, are therefore preferred; sulfur hexafluoride, organofluorides (especially perfluorocarbons) and chlorofluorocarbons are the most common.
The decomposition products of halogenated compounds are highly corrosive, hence the occurrence of corona discharge should be prevented.
Addition of sulfur hexafluoride can dramatically improve the dielectric properties of poorer insulators, e.g. helium or nitrogen.
High-voltage applications, e.g. xenon flash lamps, can experience electrical breakdowns at high altitudes.