Polymers characterized by the presence of a significant number of urethane groups. Polyurethane appears in the form of a solid foam, extremely light and with low thermal and acoustic conduction (Polyurethane foam). Among the many applications, an important use for polyurethane is packing works of art (however presenting a grave defect of flammability). In addition, for particular necessity, they may work as adhesives, taking advantage of the possibility to expand the solid foam on site.