its a medical bottle ...stainless steel...12 oz...and no the cap wont melt but the urithane seal will go out of shape if its exposed to constant gas....i drilled a small hole in the cap for venting....but scence i have the line from the tank and the canistor T'ed off, all i have to do is turn the valve of the tank on and it vents thru it...still worfking out the little stuff....at least i have no gas in the apartment....i think it burns brain cells...HA HA ...I noticed Rock Cycle now sells the canisters, with petcock....i can go to work and back...no problem...hope it gives you guys ideas...Dennis