subject: Top 10 Crown Molding Materials [print this page] Other uses for polyurethanes include: fibers, seals, gaskets, condoms, hard plastic parts, carpet underlay and sealants. Items such as domed ceilings, moldings and ceiling medallions are easier to construct of polyurethane foam rather than wood. In fact, polyurethane is considered to be the best replacement for plaster. It's low cost, lightweight and anything you can do to wood, you can do to polyurethane. It is easy to install, can be used either interiorly or on the exterior and is available in the widest range of products.