Abstract: Foamed articles are made by causing the cross-linking of a thermosetting in, preferably a polyester resin, concurrently with the production of carbon dioxide by the reaction of a carbonate with an inorganic acid. The carbonate is mixed with the resin and the acid then folded in in a progressively accelerated blending operation, whereupon carbon dioxide is generated to foam the resin, the carbonate, acid and setting time of the resin being selected to obtain an appropriate match between the progress of the foaming operation and the setting of the foam. The foam may be made in a mold coated with resin impregnated glass fibers, the impregnating resin becoming cross-linked with the foam. The impregnating resin may also be cross-linked with a resin gel coat, the glass fibers forming a tough layer between the gel coat and the foam.