Marine-Grade Plywood is a good-quality hardwood plywood made with waterproof glue. The use of waterproof glue ensures that if the plywood is exposed to moisture, or even very high humidity or boiling temperatures, the glue won’t fail, and therefore the wood layers of the plywood won’t delaminate or fall apart. Better grades also tend to be lightweight, strong, and virtually free of defects. These qualities are what make this plywood a popular choice for building boats and boat parts. It is also a smart option for durable outdoor furniture projects in coastal areas, especially when combined with a strong protective finish.
Marine plywood is not waterproof and is not pressure-treated to resist decay like pressure-treated lumber and plywood, meaning that if marine plywood will be exposed to moisture, it must be protected by a good water-resistant finish.