> What's the difference between "Helium Style" and balloons that you blow up yourself? In my limited experience with using a helium tank, we just bought regular balloons and filled those up.

I'd imagine the rubber used to make the walls of the balloon is a little bit thicker/more dense - the balloon will hold the helium in for longer (it'll take longer to diffuse through the polymer layers).

This is maybe why Silon is disgruntled by them - thicker rubber walls would make it harder to inflate...

Most helium balloons that you can buy pre-filled are made of aluminium foil as it is both lighter and the helium takes *ages* to diffuse through small flaws in the sealed edges...much longer, in fact, than the average childs attention span.

Please note I've never actually bought Smart brand balloons and compared wall densities with other brands - this just seems like the most obvious answer.

"Science week already? It must be..."

Bourne