I also have to say if you plan on working with high pressures just skip square containers.
Any propellant will do. Freon, helium, co2, regular air, compressed air, nitrogen, nitrous oxide, green gas, or butane. None of them will react with an inert plastic. The only difference that the propellant offers is whether it will... "FLAME ON" when exiting a heated plate. The opposite could happen too. It could freeze the formula.
With the innovation of the bag-on, that might not happen either.