Lumber, Plywood, and Other Wood Products - Carpenter's and Builder's Math, Plans, and Specifications - page 78

Figure 3-2 The multilayer construction of plywood gives large
thin panels greater strength and stability than solid wood. (Courtesy
of the American Plywood Assn.)
are desirable. Use of plywood may result in improved utilization
of wood, because it covers large areas with a minimum amount of
wood fiber. This is because it is permissible to use plywood thinner
than sawn lumber in some applications.
The properties of plywood depend on the quality of the different
layers of veneer, the order of layer placement in the panel, the glue
used, and the control of gluing conditions in the gluing process. The
grade of the panel depends on the quality of the veneers used, par-
ticularly of the face and back. The type of the panel depends on the
glue joint, particularly its water resistance. Generally, face veneers
with figured grain that are used in panels where appearance is im-
portant have numerous short, or otherwise deformed, wood fibers.
These may significantly reduce strength and stiffness of the panels.
On the other hand, face veneers and other plies may contain cer-
tain sizes and distributions of knots, splits, or growth characteristics
that have no undesirable effects on strength properties for specific
uses. Such uses include structural applications, such as sheathing for
walls, roofs, or floors.