Pomeranchuk cooling (named after Isaak Pomeranchuk) is the phenomenon in which liquid helium-3 will cool if it is compressed isentropically when it is below 0.3 K. This occurs because helium-3 has the unusual property that its solid state can have a higher entropy than its liquid state. The effect was first observed by Yuri Anufriev in 1965. This can be used to construct a cryogenic cooler.