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Plywood is a manufactured wood panel from the famly of manufactured boards (such as MDF,Chipboard etc.)made from thin sheets wbod veneer Plywood layers (called veneers or plys)areglued together,with adjacent plles having theuood grain rotated relative to adjacent layers up to 90 degrees.
All plywoods bind resin and wood fiber sheetallulose calls are long,strong and thin)to form a composite material This altemation of the grain is callerbss graining and has several important benefits:it reduces the tendency of wood to split when nailed at the edges;it reducesexpansion and shrinkage,providing improved dimensional stability;and it makes the strength of thepanel consistent across all direclions.There is usually an odd number of plies,so that the sheet isbalanced—this reduces warping.Because plywood is bonded with grains running against aneanother and with an odd number of composite parts,it is very hard to bend it perpendicular to the
grain direction of the surface ply.
Smaller thinner plywoods and lower quality plwoods (see Average-quality plywood photo belowand night)may anly have their plys(layers) arranged at right angles to each other,though manybetter quality plywood products will by design have five plys in steps of 45 degrees (0,45,90,135,and 180 degrees).giving strength in multiple axes.The highest quality speclalty plywoods oftenhave plys at 30 degrees (0.30,60,90,120,150,and 180 degrees)in seven layers,or have nineayers with two layers of 45 and 135 degrees in the sandwich.The smaller the step rotations theharder it is to manufacture,increasing manufacturing costs and consequently retall price.