Superfluidity in ⁴He (bosons) occurs because most ⁴He atoms gather in the lowest quantum state (Bose-Einstein condensation).
    The ³He atoms are fermions and should not be able to condense. Yet we know from superconductivity that electrons, which are also fermions, can become bosons by pair formation. The same turned out to be true also for ³He atoms. At about 2 mK they form pairs and become bosons. Bose-Einstein condensation occurs and ³He becomes superfluid.