Based on the very light weight of this stuff, I'd guess it is hydrocarbon based. A propane/isobutane blend is the most common formulation, but other hydrocarbons in various ratios can be used. If it is in fact hydrocarbon based, it will be illegal in the U.S.
There used to be lots of discussion of alternative refrigerants, and even many folks rolling their own out of propane & camping gas, over at http://www.aircondition.com
I think the bulletin board is closed, but the archived discussions are still available. Take a look at alt.ref if you're interested in this stuff.