Polyurethane (PU) glue is often a yellow glue that foams while it cures. It forms a very strong, water resistant bond. Can be used to fill holes and cracks because it expands a little bit. In addition to wood, PU sticks to a wide range of materials (e.g. paper, textile, metal, glass, plastic). The downside of PU glue is that it is a messy glue, stains are difficult to remove from wood and hands. It is also expensive compared to other wood glues such as PVA.

Polyurethanes are formed by combining a variety of chemicals. The most important ingredient is the family of isocyanates, that have not such a pretty environmental profile. Extensive exposure can cause skin irritation or allergies.