CFCs were used in a wide variety of products. Thanks to public pressure the use of CFCs by the aerosol industry declined rapidly. The other major uses were "foam blowing" for upholstery padding, freezer linings, fast-food cartons, cavity-wall insulation, and as the fluid in refrigeration and air-conditioning systems. CFCs were also used as solvents in industrial and electronic cleaning processes. Halons (bromo-fluoro-carbons) were extensively used in fire extinguishing systems. CFCs were introduced because they were generally odourless, non-toxic, stable, non-flammable and compressible substances. It was their high stability which allowed them to get into the stratosphere where they were broken down to release active chlorine. The two simplest CFCs are CFC11 and 12, which have the chemical formulae CFCl3 and CF2Cl2.