art of attaching the skin materials to the core materials these include but are not limited to welding of like materials hand lay up of fiber reinforced liquid thermoset resins onto the core surface hand lay up of fiber reinforced thermoplastic resins onto the core and the subsequent addition of heat sufficient to cause the thermoplastic resin to flow and cure to the core application of a vacuum bag to provide clamping forces to such lay ups resin transfer moulding vacuum assisted resin transfer moulding resin infusion moulding vacuum assisted resin infusion moulding vacuum resin transfer moulding compression moulding pultrusion extrusion and plate compression wafer core materials can range from a long list of materials these include but are not limited to wood end grain balsa wood foams made of polyurethane polyethylene epoxy polymethacrylimide and phenolic resins foams of the materials listed previously with various fillers such as hollow glass spheres or hollow ceramic spheres honeycomb core materials made of aluminium steel stainless steel titanium or other metals honeycomb core materials made of paper either resin coated or not produced from but not limited to fiberglass nomex u00ae kevlar u00ae wood pulp carbon graphite or other materials including but not limited to extruded or welded polypropylene polycarbonate polyethylene polyurethane polyester or other thermoplastics and pultruded extruded or welded i beams interlaced with any or all of the above mentioned materials that.