What is the difference between varnish and polyurethane?

Polyurethane is mainly used for flooring, tables, picture frames and other indoor wood items, while varnish is mostly used for exterior doors, boats, decks and other outdoor projects. Polyurethane is more durable and resistant to abrasion but is less protected against ultraviolet light damage compared to varnish.

Polyurethane is made of water or oil-based plastic resin that gives a satin or glossy finish. It is easy to apply but is more toxic than other materials. Varnish, on the other hand, is made of resins, oils and solvents. Compared to polyurethane, varnish is generally cheaper but needs more layers for a nice finish.