Liquid Tetrafluoroethane A vile of liquid tetrafluoroethane, a common refrigerant.

Refrigerants are compounds with very low boiling points and are commonly used for refrigerators and air conditioners. Their boiling points and density while in gas form can be affected by pressure, making them useful for the refrigeration cycle. The best refrigerants are those that are noncorrosive, nontoxic, and create minimal damage upon the Earth's ozone layer.

Known refrigerants can be organized by class. Class 1 refrigerants cool by changing from liquid to gas. Ones in Class 2 cool by a surrounding temperature change. And Class 3 refrigerants cool by absorbing other substances into their vapors.

Early refrigerants included toxic gases like sulfur dioxide and the leaking of these gases were the cause of many deaths. In the 1930s, Frigidaire, General Motors, and DuPont worked hard to find a nontoxic solution. They developed chlorofluorocarbons (or CFCs) such as Freon, which became the standard refrigerant for decades. However, it was discovered in the early 1980s that CFC gases cause significant damage to the ozone layer. This lead to a widespread ban on CFCs as refrigerant in the 1990s. CFCs may still be used for commercial refrigerators and air conditioners, but are prohibited for domestic use.

Since the ban, refrigerants have been made primarily of hydrochlorofluorocarbons (or HCFCs). HCFCs are only about 5% ozone depleting, compared the CFC's frightening 100%. By the year 2011, The European Union will begin to phase out refrigerants with a global warming potential (GWP) rating of 150 or more. Some of the currently-used refrigerants have a GWP rating of around 1400, though there are some more eco-friendly alternatives in development.