The noble gas helium has the lowest density after hydrogen. It is completely inert even at high temperatures, has a low solubility in molten metals and a very small atomic diameter, allowing it to diffuse through even the tiniest pores. Helium has a boiling point of -269 °C, the lowest of all gases, making it the coldest liquid on earth.
Helium (He for short) is extracted on a large scale from helium-rich natural gas sources, which are found in only a few places worldwide. Its special properties make it indispensable for many applications, for example as a lifting gas for balloons and airships, as a shielding gas for welding, as a tracer gas for leak detection or as a carrier gas in gas chromatography.