While conventional exterior wood finish products are petroleum-based and high-VOC, Vermont Natural Coatings exterior wood finish is derived primarily from whey, a by-product of cheese making and a renewable resource. Its formadelhyde-free and low-VOC formula provides a clear waterproof finish and protects against mildew, mold, harmful UV rays, and cleans up easily with soap and water.
According to the manufacturer's information, "PolyWhey natural wood finishes are twice as hard as the conventional water-based polyurethane products you'll find at most stores. They dry fast, they don't yellow over time, and there's no noxious odor... Its VOC levels are lower than the strictest U.S. indoor air quality standards, with levels below 180g/L (grams per liter). That's 25% less than the VOC standard that other water-based finishes try to meet."
$59.99 per gallon from EcoHaus.