Why do Helium baloons defalte so quickly

[fishbait]

Why is that? are helium Molecules smaller than air or of a higher pressure than air? Also posted on seasonal wonder which brain boxes get this first.

[gen2]

In two words: Yes, both.

The gas inside the balloon is at a higher pressure than the air outside and helium atoms are the second smallest, only beaten by hydrogen - but whereas helium gas is made up of atoms, hydrogen is diatomic and goes around as molecules of H2.

The helium atoms easily diffuse through minute pores in the rubber membrane of the balloon.

[squarebear]

gen2 is quite right. This is why most helium balloons are made of metal foil as it's harder for the helium to pass through the surface.

[voyager1970]

I agree with the size issue, but the pressure of the gas inside the balloon must be the same as the pressure outside. If the pressure is higher inside the balloon would explode!

[floggedhorse]

Sorry to disagree - but surely the pressure in the baloon is greater than the pressure outside - it has to overcome the restrining force of the baloon material!