The right answer is chlorofluorocarbons (CFCs).
A good aerosol propellant must be odorless, colorless and non-flammable. CFCs, chlorofluorocarbons, have been used for many years. Unfortunately, they would have actively participated in the destruction of the ozone layer. Their use was banned in 1985 by the Montreal Protocol. Other often flammable substitutes (for example butane or propane) have been found.
