 These might consist of forming a frame using thin planks of a light wood such as balsa to duplicate the formers, longerons, spars, and ribs of a vintage full-size aircraft, or, on larger (usually powered) models where weight is less of a factor, sheets of wood, expanded polystyrene, and wood veneers may be employed.Regardless of the underlying structure, it is then skinned and subsequently doped to provide a smooth sealed surface.For light models, tissue paper is used.