Sulfur hexafluoride (SF₆) has a density of 6.12 g/L at sea level, considerably higher than the density of air. It's therefore allowing experiments like this one, where soap bubble are apparently 'suspended' over a tank

\[source: buff.ly/3HaEjcb (https://buff.ly/3HaEjcb)\]

https://nitter.moomoo.me/Rainmaker1973/status/1647536937266233345#m