WBP stands for Water Boil Proof. WPB is the best type of weather resistant plywood. Structural plywood is Structural plywood is manufactured from hardwood as well as softwood veneers. Based on the quality of the face and back veneer, it is classified in terms of quality from A to D. Essentially, structural plywood makes use of A-Bond and B-Bond glues. Structural plywood is best suited for external applications, since it doesn’t become weak when exposed to any changes in the weather.