At sea level the air is pressing on the bottle at 14.7 psi per sq. in. So at the edge of space the cylinder would only have 14.7 PSI more pushing against the inside of the or in actuality have 14.7 psi less pushing against the outside of the bottle, no problem! Now USPS I believe has a reg against shipping anything with pressure in it. Have people shipped guns with pressure in them, yes. But is it against the regulations, I believe so. I've had a retailer send me a lead acid battery through the mail before which I know for a fact is against USPS regs.