Expanded products, more specifically, rigid or semi-flexible foams of low density from 1.5 to 12 lbs/ft3 or more, with closed cells can be manufactured. The products have a PVC backbone with branches with methacrylate crosslinked with isocyanate through a reaction activated by ultraviolet or microwave radiation. The use of polyfunctional monomers that are sensitive to irradiation yields a higher cross-link density, which improves the physical and mechanical properties such as hardness, resistance to abrasion, ductility, and resistance to friction. The selection of monomers and oligomers allows the manufacturer to determine of the final properties of the foam. The process yields foams with extreme hardness and better shear factors making the foam an ideal product for aerospace and windmill use. These physical properties emerge during the post-curing process, preferably by use of compounds based on methacrylates in dispersion with PVC and isocyanates.