Marine-Grade plywood is not waterproof or pressure-treated. Its exposure durability rating is EXTERIOR and the glue used is a water-resistant structural adhesive. "Marine" grade indicates that it is made from high-quality hardwood and with waterproof glues. It is a great option for outdoor projects and in coastal areas. It is still recommended that you finish the exposed surfaces with the appropriate exterior finish.
Specially designed plywood panel made only with Douglas-fir or western larch, solid jointed cores, and highly restrictive limitations on core gaps and face repairs
Brand / grade may vary by availability and store location
For boat-building applications, a special grade of plywood, APA Marine Exterior, is available. Marine-grade Plywood is a premium panel using the same fully waterproof glues as regular Exterior plywood, but manufactured with only Douglas-fir or Western Larch veneers, and with additional restrictions on veneer grade, core gaps, patches and other characteristics.