[bubal7 (OP)]

Since butane is denser than air, soap bubbles float on an atmosphere of butane

newbielink:http://www.youtube.com/watch?v=IF9rWzOxWtY [nonactive]

Butane density 2,52 Kg/m3
Air density 1,20 Kg/m3

So butane is twice as dense than air.