Name That Gas!!! (please??)?

Question

Ok, i saw this on Mythbusters, and i can't remember the gas that he used.

ok, helium makes your voice high, and gas (x) makes your voice deeper. (six times the density of air)

what is gas (x)??

Answer 1

sulfur hexafluoride.

Answer 2

go here:

http://watchmythbustersonline.net/