  Matter implies the existence of a large-scale connected cluster of a uniform
nature. The appearance of such clusters as function of hadron density is
specified by percolation theory. We can therefore formulate the freeze-out of
interacting hadronic matter in terms of the percolation of hadronic clusters.
The resulting freeze-out condition as function of temperature and
baryo-chemical potential interpolates between resonance gas behaviour at low
baryon density and repulsive nucleonic matter at low temperature, and it agrees
well with data.
