Q. How long do foil balloons last?

Answer

Mylar (foil) balloons can keep their shape and volume for 3-5 days under ideal conditions. They'll float for at least two weeks. These balloons could deflate under air conditioning, but if they're exposed to warmer air, they'll be fine again. Balloons exposed to high temperatures and intense sunshine may burst after only one hour. When exposed to low temperatures, helium molecules contract, causing balloons to deflate faster and not float as high. Because the constant flow of air around for a balloon increases the rate during which helium atoms leave through into the walls of the balloon, the balloon's flying time is reduced whether it is indoors or outside.