Sulfur Hexafluoride

Sulfur Hexafluoride is an inorganic, colorless, odorless, non-toxic and non-flammable gas (at room temperature and pressure).

You can do a lot of fun scientific experiments with sulfur hexafluoride. Aside from making your voice much deeper when you talk or sing by breathing in a lungful of SF6 , you can also float your ship visibly with nothing. It's cool!