Marine-grade plywood is considered the best plywood for waterproof applications. This type of plywood is made with waterproof glue and is designed to withstand the harsh conditions of marine environments, including exposure to water, salt, and humidity.

Marine-grade plywood is typically made from high-quality hardwoods, such as birch, mahogany, or oak, which have natural resistance to water and decay. It is also usually constructed with more layers and thicker veneers than standard plywood, which makes it stronger and more durable.

It is important to note that even with marine-grade plywood, proper sealing and finishing techniques should still be used to ensure maximum waterproofing and protection against moisture.