Helium (He) is the second lightest elemental gas next to hydrogen. Colorless, odorless, tasteless, nontoxic and chemically inert, helium is nonflammable and has a high thermal conductivity.

It is used to create an inert gas shield and prevent oxidation during welding of metals such as aluminum, stainless steel, copper and magnesium alloys. The addition of helium generally increases weld pool fluidity and travel speed.