  We give an analytical description of the spatial distribution of domain walls
produced during a biased nonequilibrium phase transition in the vacuum state of
a light scalar field. We discuss in detail the spectrum of the associated
cosmological energy density perturbations. It is shown that the contribution
coming from domain walls can enhance the standard cold dark matter spectrum in
such a way as to account for the whole range of IRAS data and for the COBE
measurement of the microwave background anisotropy. We also demonstrate that in
case of a biased phase transition which allows a percolative description, the
number of large size domain walls is strongly suppressed. This offers a way of
avoiding excessive microwave background distorsions due to the gravitational
field of domain walls present after decoupling.
