  We report on our recent work about the description of a meson gas below the
chiral phase transition within the framework of Chiral Perturbation Theory. As
an alternative to the standard treatment, we present a calculation of the quark
condensate which combines the virial expansion and the meson-meson scattering
data. We have also calculated the full one-loop elastic pion scattering
amplitude at finite temperature and we have unitarized the amplitude using the
Inverse Amplitude Method in order to reproduce the temperature effects on the
mass and width of the $\rho$ and $\sigma$ resonances. Our results show a clear
increase of the thermal $\rho$ width, as expected from previous analysis. The
results for the $\sigma$ are consistent with Chiral Symmetry Restoration. We
comment on the relevance of our results within the context of Relativistic
Heavy Ion Collisions.
