Definition

• Plywood is sold by thickness in either sanded or unsanded sheets. Sanded boards are usually sold in 1/4-inch increments; unsanded in dimensions measured in 16ths or 32nds of an inch. Therefore, 17/32 plywood is an unsanded board -- when sanded, it will be approximately 1/2 inch. However, quite a wide tolerance is given for plywood thickness and "actual" dimension varies quite considerably between products marked with the same nominal dimension. Expect 17/32 plywood to measure anything between 18/32 inch and 1/2 inch.
  
  

Construction

• Plywood's layered construction explains the variability in dimension: both the qualities of the different layers and the degree of compression are unpredictable. Any defect in one veneer will be transferred under pressure to adjacent layers. The component woods also shrink or expand depending on humidity. Layers are glued together with a glue containing phenol formaldehyde. This is water resistant, making many plywoods suitable for external applications. The highest-quality ply with the greatest water resistance is marine ply.
  
  

Types

• Plywood may be exterior or interior grade; softwood or hardwood. Softwood ply is always constructed of layers of differing veneers. The top layer may be chosen for its color or grain. Hardwood plywood similarly has a high-quality outer veneer -- perhaps oak, teak or mahogany. Veneer core plywood is termed VCP, but hardwood plywood may have solid lumber or medium-density fiberboard (MDF) cores instead. High-density plywood (HDP) is usually of maple or birch; it has fewer voids than standard plywood.
  
  

Grade

• Plywood is distinguished by quality as well as thickness. The best grade is A; grade B is permitted a few more imperfections. The poorest grade is D, which features many knots and voids within the layers. Plywood is given a three-letter code, referring to the quality of its front, core and back. ACC has one good face over an inexpensive core and reverse side. ACA has two good sides. Sometimes numbers are used: A1 signifies two good sides; A4 one good side and an inferior reverse. Plywood may also be coded according to wood type; for example, DFP for Douglas Fir Plywood. Imports using different grading codes add to the complexity.
  
  

Uses

• Most commonly, 17/32 plywood is softwood, construction grade. It is used for wall sheathing, subflooring and similar applications. It is inexpensive and versatile. At just over 1/2-inch thick, it is a strong, heavy, warp-resistant board. As a wall sheathing, it resists wind and earthquake. The unsanded 17/32 dimension is appropriate since it will be covered with other materials. For the same reason, CCC is a common grade for sheathing ply. The more expensive hardwood ply is less commonly available in 17/32 -- comparable hardwood products would usually be 1/2 inch.