The first type of finish, often called “film-forming,” actually sits on top of the wood, and if you’re after a rich, lustrous finish with a glossy look, this is the finish for you. These products are labeled as spar varnish, exterior polyurethane, or alkyd resin, among others.
Most people think film-forming finishes are only clear, but you can also get them with added color. They’re a popular choice for classic outdoor furniture like wood tables and chairs, since people are used to seeing a glossy, built-up finish on these.
While they look great, even a high-quality film-forming finish is prone to peeling over time. And when it’s time to refinish the wood, the finish can be difficult to remove.
If you want an option that’s easier to refinish, then a penetrating oil finish might be the right type for you. This type of finish is also sold as deck stain or outdoor oil.
Penetrating oils get applied like standard wood stain but contain mildewcides, UV blockers, and other ingredients for outdoor use. Though they come in a variety of colors, the trade-off is that they don’t have the rich luster of a film-forming finish.