BOARDS INDIA

Most types of wood eventually get damaged in case of a prolonged exposure to water. However good quality waterproof plywood is built in such a way that it offers a better degree of resistance to water, compared to natural solid wood or commercial MR grade plywood. The reason for this is that a phenolic resin, which is a synthetic plastic resin, is used for gluing all the individual plies together. Use of synthetic plastic resin helps in making the plywood waterproof.

Most countries have their own grading system. In India, 'BWR grade' plywood means waterproof plywood. BWR stands for 'Boiling Water Resistant'. 

Waterproof plywood (BWR grade) is different from Marine plywood. Marine plywood is specifically built so as to resist a prolonged exposure to water. Quality tests for marine plywood involve submerging a sample piece in boiling water for a period of 72 hours, and then checking its strength and other properties.

Marine plywood is costlier than waterproof ply and used for marine applications such as for constructing boats and ships. For making office or home furniture, marine plywood is usually an overkill, and good quality waterproof plywood serves the purpose in most cases.
In case of outdoor use, selecting Marine ply or Waterproof is a decision to be taken on a case to case basis, depending on the intended application. For example for the purpose of roofing, marine plywood would be better.