Abstract: Composite formed boards made of plastic and organic material with a fibrous structure are described. The composite is a foamed mix having a density lower by at least 10% and preferably 20%, than the density of a solid organic-plastic composite made of the same components. The foamed mix is bonded permanently and inseparably with a solid plastic layer, at least from a side opposite to a homogeneous rubber-polyurethane composite. The thickness of the solid plastic layer is smaller than that of the organic-plastic layer (preferably at least five times and most preferably at least fifteen times) and that of the rubber-polyurethane layer (preferably at least fifteen times and most preferably at least twenty-five times). The solid plastic layer may have a grooved structure or an impressed structure with a concavity directed inwardly. The solid plastic layer is preferably bonded with the organic-plastic layer by a co-extrusion joint.