well, don't really know if it's physics or chemical... gas lighter than air, to be used in a ballon who can fly up by itself. I only know 3 types: helium, hydrogen, hot air Are there other, can be used in a ballon? And how can I calculate how much updrift the gas creates or better, how much weight can how much gas raise? What is the best gas to be used? I mean, the less gas needed, but the most updrift generated. Any suggestions?