A common term for plywood is the number of layers, such as 5-ply, 7-ply, etc. These are the number of veneer layers that make the plywood.
The number of layers used varies, but are always in odd numbers. This is because the two outer layers of the veneer must run in the same direction to keep the panel balanced.
Plywood of the same thickness but with different layers can be used. For example, a 3/4 inch piece of plywood can have either 7 or 11 layers.
Since they are both the same thickness, the 11-ply plywood will have thinner core veneers. This means more layers with more glue, leading to fewer voids, more rigidity, and stronger boards. The fewer voids also allow you to leave an exposed edge on plywood and have a much better appearance. Birch Plywood is the best example of this.
As the number of layers increases, so does the cost. The number of layers chosen depends on the final application.
