  4-dimensional homogeneous isotropic cosmological models obtained from
solutions of vacuum 5-dimensional Einstein equations are considered. It is
assumed, that the G(55)-component of the 5-d metric simulates matter in the
comoving frame of reference. Observable 4-d metric is defined up to conformal
transformations of the metric of 4-d section \tilde{g}, with a conformal factor
as a function of the component G(55). It is demonstrated, that the form of this
function determines the matter equation of state. Possible equations of state
are analyzed separately for flat, open and close models.
