  A fluid of domain walls has an effective equation of state $p_w = -
{2/3}\rho_w$. This equation of state is qualitativelly in agreement with the
supernova type Ia observations. We exploit a cosmological model where the
matter content is given by a dust fluid and a domain wall fluid. The process of
formation of galaxies is essentially preserved. On the other hand, the
behaviour of the density contrast in the ordinary fluid is highly altered when
domain walls begin to dominate the matter content of the Universe. This domain
wall phase occurs at relative recent era, and its possible consequences are
discussed, specially concerning the Sachs-Wolfe effect.
