Freon 11, also known as R-11, CFC-11, or by its scientific name trichlorofluoromethane, is a colorless and odorless gas that was used mostly as a refrigerant until the early '90s. Due to its potential to deplete the ozone layer, it is no longer being produced as of January 1996.
Freon 11 was also used as a propellant for aerosols until the 1970s, when it was banned because of its harmful effects to the ozone layer. Most equipment produced in the '90s that used Freon 11 is being replaced by its more environmentally-friendly substitute, R-123. Even though it is less harmful, even R-123 is set to be discontinued in 2020.