1. Freon, also known as Freon, whose name comes from English Freon, is a registered refrigerant trademark of DuPont Company in the United States. There are differences in the definition of freon in China, which is generally defined as the general name of 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 (CCl_F_, that is, R 12, a kind of CFC).

2. 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.

3. The use of chlorofluorocarbon refrigerants such as dichlorodifluoromethane has been restricted because they will destroy the atmospheric ozone layer. There have been many holes in the ozone layer on the earth, some of which have exceeded the area of Africa, which is largely due to the chemical properties of chlorofluorocarbons. Another harm of freon is the greenhouse effect.