Will helium balloons get ruined if you ship them via airplane? I want to send a party in a box to my sister-in-law, but I don’t want the balloons to be fagged out or broken when they arrive. I will use the shiny ones as opposed to the rubber ones. Anyone know?
If they’re deflated when you send them, I can’t anticipate any problems. But if they’re inflated, I would be surprised if they stayed intact. Even pressurized airplanes are typically only pressurized to the air pressure at 8000 feet above sea level, which is only about 75% that of sea level. Latex balloons would respond to this by increasing in volume by about 33% (this is a change in radius of about 10%), which may well be enough to burst them. Mylar balloons don’t generally have the opportunity to expand further, unless they’re underinflated to start with, so the mylar would be supporting a pressure difference of about 25,000 Newtons per square meter, or 3.7 psi, which I think would be enough to cause a leak.
On the other hand, if Shangrala and your SIL’s house are both at high altitude, this might not be as much of a problem. If the starting point and destination are both at 8000 feet, and the balloons are properly inflated at your place, then there shouldn’t be any problem at all.
Over the years I have seen many people take balloons on airliners. I have yet to see one burst, but they always have that tired 4 day old look at the end of the flight. You know the one, where the balloon is about 25% deflated, and looks tired and neglected. 
The bastards had better give you a discount on your ticket too! 
Unfortunately, I will not be accompanying the balloons to the party. They will probably be riding in the cargo area. Damn! I was hoping they’d float out of the box when she opened it up. Maybe I can send them by bus! The Mylar balloons tend to stay inflated forever. I’ll have to look into that. Thanks for your responses!
Is it not possible to jsut send them with ground shipping? Granted, the extra time taken may still acuse the balloons to leak to a small extent, but surely that’s better than possible poppage?
I was on a flight during which a mylar balloon in one of the overhead racks did burst. The noise of this certainly got everyone’s attention.