Plywood for exterior use is a built-up board of laminated wood veneers in which adjoining plies are bonded together with the grain at right angles, under heavy pressure with waterproof glue.
Exterior plywood may be applied over sheathing paper and nailed to the studs or applied over an existing outside wall surface.
It should be protected from the weather by coating with good spar varnish or painting with outside house paint.