Ultra-Violet Light – Often called black light; this is at the lower range of the spectrum and not visible; causes destruction of paint films.

Ultra Violet Absorber - A substance used in some exterior coating that absorbs UV radiation, and reduces or delays damaging UV effects from sunshine to the coating or substrate.

Ultra Violet Radiation (UV) - The portion of the radiant energy of the sun’s spectrum that causes damage to coatings and sealants and to the surface of unprotected wood.

Ultra Violet Resistance - The ability of a coating or sealant to remain undamaged when subjected to UV radiation, as from direct sunlight.

Undercoat/Undercoating - A coating, generally pigmented, that provides improved adhesion and/or maximized gloss and uniformity of a finish coat when used on bare wood.

Undertone – The color of a paint seen by transmitted light.

Union – A combination or regrouping together for specific purposes.

Universal Color – A colorant liquid of paint consistency compatible with most types of paint vehicles.

Urethane - A type of binder used in coatings. Characterized by excellent flexibility and chemical resistance.

Urethane-Modified Alkyd - An alkyd that has been chemically modified for improved flexibility and chemical resistance. A binder used in “polyurethane” varnishes.

Urethane Resin – A two-component resin system with excellent flexibility and chemical resistance.

U.S. Gallon – A unit of volume equal to four liquid quarts, eight liquid pints, 231 cubic inches, or 3.785 liters. One U.S. gallon of water weighs 8.33 pounds (3.78 kg).