The common refrigerants in traditional industry and life are partially halogenated hydrocarbons (especially chlorofluorocarbons), but now they are gradually eliminated because of ozone hole. Other widely used working media are ammonia, sulfur dioxide and non-halogenated hydrocarbons (such as methane).

Freon is generally defined as the general term for halogenated compounds of saturated hydrocarbons (mainly methane, ethane and propane). According to this definition, freon can be divided into four categories: CFC, HCFC and HFC. Some scholars define freon as CFC refrigerant; [1] In some data, freon only refers to dichlorodifluoromethane (CCl2F2, R 12, a kind of CFC).

Freon is colorless gas or volatile liquid at room temperature, tasteless or slightly smelly, non-toxic or low-toxic, and its chemical properties are stable.

The use of chlorofluorocarbon refrigerants, such as dichlorodifluoromethane, has been restricted because they will destroy the atmospheric ozone layer.