Can a balloon really stay inflated for 17 years?

Question

my sister's friend told me that she has one of those metallic balloons that was filled with helium on the day she was born. her dad brought it to the hospital as a gift. she is 17 years old now and she claims it is still inflated! she says it doesn't float, it just lays on the floor but it's still inflated! is this possible? could the helium have been somehow exchanged for regular air and kept the balloon inflated? this girl's mom also swears it's true.

Answer 1

Not a mylar balloon expert, but from what I know 17 years is certainly much longer than they typically last (a few days). I would be very surprised if the balloon were still firm, however if it just still has a generally filled-out shape I could believe it. I think much depends on how much the balloon is handled.

Unlike a latex balloon, mylar balloons don't stretch much when inflated, so there is no inherent pressure forcing the gas out of the balloon. Being filled with helium, the interior of the balloon is actually going to be at a lower pressure than the outside air so there is a possibility that air could seep into the balloon over time.

If the balloon isn't handled, enough air could seep in to neutralize the buoyancy of the helium (causing the balloon to sink) while not affecting the overall shape of the balloon. Once the pressure inside vs. outside the balloon is neutralized, any pressure applied to the balloon (like a person squeezing it) would irreversibly force some of the air/helium mixture out of the balloon.

So I'd say yes, it's possible.

Answer 2

Not an answer to your question but I have a ladybug balloon inflated with air that was given to me along with several other balloons (spider, grasshopper, etc). I have had them for 7 years or so and the ladybug is still firm enough to sit on. All the others have pretty much deflated. But these are some sort of plastic stuff though and not that metalic stuff.