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Commercial plywood vs. Marine plywood

There is a big difference between commercial plywood and marine plywood, not only in quality and characteristics, but also in costs. This article compares these two types of plywood.

Commercial plywood Marine grade plywood
Commercial plywood is of MR grade (Moisture resistant) grade. Note that 'moisture resistant' is not the same as being 'waterproof'. It only means that the plywood can withstand some amount of moisture, dampness and humidity. Marine plywood is a completely waterproof plywood, that has been specifically manufactured for marine applications.
Indian standard for Commercial ply is detailed in document IS:303 Indian standard for Marine plywood is specified in document: IS:710
The adhesive used for bonding the plies together is Urea formaldehyde. Unextended phenolic resin is used for bonding the plies together. Unextended means undiluted. Phenolic resin is a synthetic plastic resin made from phenol formaldehyde and it makes Marine plywood completely waterproof.
Commercial plywood is most commonly used in the making of home and office furniture, and interior decoration work such as paneling, partitions and the like. Marine plywood is used for building boats and ships, and any other applications in which the plywood is sure to get a large amount of exposure to water.
It is an Interior grade plywood that is meant for indoor use. Marine plywood is of Exterior grade and meant for extreme exterior uses. Its also better than the Exterior grade BWR (Boiling Water resistant) plywood that is used for making kitchen furniture.
Cheaper compared to Marine plywood. It is a lot costlier than Commercial ply.
Its strength is weaker compared to the strength of Marine ply. It is much stronger than Commercial grade plywood because of the superior wood and glues used in its manufacture.

Note that the shopkeepers in India, often refer to External BWR grade plywood as Marine ply. For them Commercial ply means MR grade, and Marine ply means BWR grade, (though strictly speaking that's inaccurate). For the difference between these two types read MR grade plywood vs. BWR plywood

for more information.