Terms of the Trade: What Is Polyurethane Varnish?

A can of polyurethane varnish.

Polyurethane varnish is a synthetic material that's essentially a liquid plastic. When applied onto the surface of wood it provides a durable high gloss finish that protects the wood from a variety of foes including fungus, mold, and moisture. Polyurethane varnish comes in a variety of options including water and oil-based varieties, and satin and glossy finishes.