What happens to released helium balloons?

While at Vail's Sunday Market, Shirlene and I saw a released yellow balloon and wondered what would become of it? Does it eventually pop? Fly forever? Slowly return back to the ground? Get eaten by birds mistaking it for candy? Well, actually...

1. When let go, they rise at a rate of 2-m/s
2. After 1.5 hours they reach an altitude of 5 miles
3. At this point, the temperature is about negative 40 degrees C - because its so cold, the balloon becomes mad inelastic.
4. Simultaneously, while rising, the atmospheric pressure decreases and since the pressure in the balloon is the same, it gets larger.
5. Eventually, there's a point where the balloon becomes too inelastic and the pressure keeps pushing to increase the volume of the balloon.
6. Wait for it...
7. POP

And now you know.