What is the average lifespan of a helium balloon?

Question

I went to homecoming with a girl named Karrie, on October 13th, 2007. I asked her to be my girlfriend the same night. I got her a balloon that she wanted inflated with helium from inside of the school. It was yellow with stars on it, her favorite color and shape. We are still dating now, and strongly in love, and we've never had a problem yet, and we are constantly with each other. The balloon is still perfectly inflated to this day, with no loss of air or loss of shape. Would this be normal, or what could be the explaination?

Answer 1

It is unusual since helium atoms are so small they can penetrate the balloon and escape.

Answer 2

I hope your relationship lasts longer than the balloon!  If the balloon material is extremely light and not elastic, there's no particular process to make it lose its shape.  But over time, the helium diffuses out, and the gas mix inside equalizes with that outside.  So I'm sure it's no longer lighter than air.  That seldom lasts more than a few days.

Answer 3

This is normal if the balloon is metallic or foil.