Polyurethane bumper covers, like the one on this old Camaro, are rare on late-model cars. However, with more people restoring vehicles from the 70s and 80s, the need to repair and restore polyurethane has grown.
Polyurethane is a thermoset plastic. During the molding process, two chemicals are mixed and injected into the mold, forming a solid through a chemical reaction. As a result, thermoset polyurethane is non-meltable, so nitrogen welders cannot be used to make a fusion weld. Instead, an airless plastic welder can be used to create a hot-melt glue-style repair.
