What's inside a "dead" helium balloon?

After a few days, children’s party balloons all end up on the floor, but I’m mostly referring to the rubber stretchy ones, not the metallic shiny ones.

I know that helium can escape through the walls of the balloon, but it seems that a balloon that has retained most of its volume should remain buoyant.

Also my home experiment on a “dead” balloon does not seem to give the expected high voice.

So therefore, I assume that either a) the helium was very impure to begin with, or b) some other gas (N2?) is also diffusing into the balloon at the same time.

What say you?

I missed the edit window, but I just tried again with a balloon from Saturday morning which has been on the floor for maybe 6 hours.

It gives a barely perceptible and very slight voice alteration, very different from a “fresh” balloon.

The air will try to establish an equilibrium. The balloon starts out with high pressure, so equilibrium will strongly favor helium leaving the balloon. You don’t have to lose very much before it affects buoyancy. As the pressure inside comes closer to the pressure outside, the situation looks more like an even exchange, with helium coming out and regular air going in.

A tied off balloon is not a closed system, so there is gas exchange between the inside of the balloon (He) and the outside of the balloon (Air).

Eventually enough helium diffuses out and enough room air in that the balloon is no longer bouyant.

Just because the net flow of gas is outward, it doesn’t mean that there is no flow of gas into the balloon. Rivers have a detectable salt content well before they empty into a salty body (e.g. ocean). I keep my glovebox under a positive pressure of nitrogen, but it still gets oxygen in it. Helium out + air in eventually leads to a buoyancy that is equal to and then less than the weight of the balloon and string.

Sort of. The balloon starts out with a high partial pressure of helium compared to the rest of the atmosphere. The absolute pressure in the balloon is nearly identical to that outside of the balloon; the additional pressure created by the elastic balloon walls is fairly small. Otherwise, yes, the high helium partial pressure forces helium out of the balloon, while the high oxygen and nitrogen partial pressures force those gasses into the balloon. The balloon material is, I believe, more permeable to helium than the other gasses, so helium wins the race.

You… what?

Like, a chemical glove box, not the glove compartment in a car.

Ohhhhhh. Lol. Thank you.

Except the gloves on my glovebox are not limp like that, no sir! Firm and erect, like here. Just about bursting with nitrogen and all sorts of heinous vapors that have leaked out of their containers.

Your own private army of Heil Rukens!