The ribs across the mould have two purposes: first, to keep the mould from buckling under the weight of the wet pulp, and second to speed the moulding process, as the shape of the ribs, pointed on top, causes a series of vacuums to occur when the mould breaks water, thereby pulling the excess water quickly down through the wire covering of the mould. In a modern paper-making machine the squeezing of the wet paper against felts is done mechanically through a series of rollers.
