My understanding is it's a varnish with a lot of mineral spirits added to it. Wood finishers call this wiping varnish Varnish is a mixture of a drying oil (e.g. Linseed) a resin (today usually polyurethane) and a thinner. If you cut spar varnish 50/50 with mineral spirits that's about what Tru-oil is. I will say it's a good product and you don't have to buy an entire quart just to finish a stock.