Smooth surfaced panels e.g. of oriented strand board are prepared by producing a thin uniform mat of high density made from bonded wood particles, fibers or strands. The mat is produced by passing it between a pair of rollers one of which is heated to produce a smooth cured surface on the corresponding side of the mat, and the other of which is unheated, the corresponding side of the mat containing uncured adhesive. The mat is subsequently bonded to a panel, e.g. an oriented strand board core under conditions of heat and pressure to produce a composite panel having a smooth surface.