A dielectric gas, or insulating gas, is a dielectric material in gaseous state. Its main purpose is to prevent or rapidly quench electric discharges. Dielectric gases are used as electrical insulators in high voltage applications, e.g. transformers, circuit breakers (namely sulfur hexafluoride circuit breakers), switchgear (namely high voltage switchgear), radar waveguides, etc. The most common dielectric gas is air, due to its ubiquity and low cost. Another commonly used gas is a dry nitrogen. Dielectric gases can also serve as coolants. Vacuum is an alternative for gas in some applications.