The flow between rough surfaces in sliding motion with contacts has been analyzed through the volume averaging method for different geometries of surfaces, including the self-affine geometry encountered in cold rolling. In this paper, we simply give an overview of main results. An average flow model is derived, in which the influence of roughness is taken into account through effective transport tensors called "flow factors" . The flow factors have been determined for various deterministic (sinusoidal) and random roughness distributions.