If you take helium gas and you cool it at atmospheric pressure to 4.2 K in becomes a liquid. Keep cooling to 2.2 K and the helium enters its superfluid phase, called helium II. Superfluid helium has several very useful properties and is used in science and technology in multi-tonne quantities today. In particular, helium II is an exceptionally good conductor of heat and this combined with its low temperature means that the superfluid is ideal for cooling components made from superconducting materials.