Marine grade plywood is essentially the highest-quality plywood you can get. It’s called “Marine grade” in part because it has to be fully capable of standing up to rain, snow, and moisture on a regular, repeated basis in order to qualify. This isn’t the only qualification a piece of plywood needs to meet to be labeled as marine grade, however.
Marine grade plywood can only be made with Western Larch or Douglas Fir wood. It also must have 5 or more layers, with far fewer air pockets and small voids than regular plywood. It can have some knots in the exterior plies, but no knotholes are allowed. It must be bonded with waterproof glue.
You might expect to see Marine grade plywood used in the installation and construction or birdhouses, furniture, boats, siding for buildings, signs, pergolas, gazebos, and more. Because Marine grade plywood is able to withstand 24/7 immersion in water, you’ll find it in many different docks, piers, boats, lighthouses, and other buildings and features that are constantly exposed to a high level of moisture.
Bathrooms, kitchens, patios, decks, and porches are also commonly built with at least some Marine grade plywood during construction. These are household areas that see a lot of water and moisture, thus Marine grade plywood makes an excellent choice for their construction.