The explanation that came with this on YouTube says:
Get enchanted by a aluminium foil ship floating above ground on hexafluorid (gas significantly denser than air) at the Physikshow of the University of Bonn!
I looked on the Really Weird Materials site Alex posted earlier, but found no explanation of â€œhexafluoridâ€. I Googled the word, and found plenty of documentation, none of it in English, at least what a non-scientist would understand. Can someone direct us to more on this? Push play or go to YouTube. -via Arbroath
What they have is Sulfur hexafluoride. Itâ€™s 5.11 times as dense as air. Itâ€™s non toxic, although itâ€™s byproducts can be extremely dangerous.
Another interesting point is that inhaling this gas will make your voice sound deeper. Sound does not travel as fast in this medium. Helium can transmit sound very rapidly, hence making your voice squeaky.
Thanks, Russell! I knew someone would know more about it!