  We discuss two models for describing the behavior of matter at large
densities and intermediate temperatures. In both models a softening of the
equation of state takes place due to the appearance of new degrees of freedom.
The first is a hadronic model in which the softening is due to chiral symmetry
restoration. In the second model the softening is associated with the formation
of clusters of quarks in the mixed phase. We show that both models allow a
significant softening but, in the first case the bulk modulus is mainly
dependent on the density, while in the mixed phase model it also strongly
depends on the temperature. We also show that the bulk modulus is not vanishing
in the mixed phase due to the presence of two conserved charges, the baryon and
the isospin one. Only in a small region of densities and temperatures the
incompressibility becomes extremely small. Finally we compare our results with
recent analysis of heavy ion collisions at intermediate energies.
