  We consider a covariant approach to coarse-graining a network of interacting
Nambu-Goto strings. A transport equation is constructed for a spatially flat
Friedmann universe. In Minkowski space and with no spatial dependence this
model agrees with a previous model. Thus it likewise converges to an
equilibrium with a factorizability property. We present an argument that this
property does not depend on a `string chaos' assumption on the correlations
between strings. And in contrast to the earlier model, this transport equation
agrees with conservation equations for a fluid of strings derived from a
different perspective.
