What is Marine Grade Plywood?
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.

How is Marine Grade Plywood Made?
Marine grade plywood is made by arranging 5 or more plies of Douglas Fir or Western Larch wood in a perpendicular manner so that the grains are alternating from vertical to horizontal. This perpendicular arrangement of the individual plies is what gives the plywood increased strength.

The plies are bonded together under heat and pressure, using a special type of glue that is waterproof. A water-resistant finish is then added to the exterior. The waterproof glue as well as the lack of voids, knots, and air pockets are the defining features that separate Marine grade plywood from various other types of plywood.

Also, the fact that Marine grade plywood is made with more, thinner layers of high-quality wood as opposed to fewer, thicker layers of lower-quality wood is what sets it apart from other types of plywood.

Marine grade plywood is not to be confused with similar types of plywood like pressure-treated plywood. While Marine grade plywood is technically “pressure-treated”, it is not soaked in or made with any special chemicals that increase its resistance to rot, mold, and moisture. The term “pressure-treated” is usually used to refer to plywood that has, in fact, been chemically soaked to improve its durability.