Halon 1211and 1301are a type of refrigerant, one of the nasty ones that has been banned. It is still available and it is still cheaper that the current halon alternatives (fe-36). What is good about halon it comes out of the extinguisher as a gas and leaves no residue behind, that means that there is no powder to clean off. If you ever spray a standard ABC powder on aluminum wash it off quickly as it will corrode it. For a more complete explanation of how halon and fe-36 work go to http://www.dupont.com/fire/