Plywood Cores come in many varieties
The core of a plywood panel is the largest component and therefore plays the largest role in how that panel will perform. As I mentioned in the first episode of this series on plywood, you need to choose your panel based on what is most important for the application. So it is imperative that you understand the core construction and how that will change to working properties of that particular sheet of plywood. Plywood cores dictate everything.
There are 4 basic types of plywood cores: veneer core, lumber core, composite core, and combination (combi) core. The last one has a few variations based on whether the composite is used as cross bands or as the central core. Each of these plywood core types has strengths and weaknesses. For instance, composite cores give us the best flatness and best surface uniformity. But veneer core is the best with stability and screw holding.
This is where combi cores come into play as we try to blend the best attributes together to create the toughest, flattest, most stable plywood panel around. Again this all depends on what is most important to your application. One could have the best of all worlds and create the absolutely perfect plywood panel that excels in all factors but they you would be looking at a VERY expensive sheet of plywood with limited availability. The fact is none of use actually needs that perfect panel and jiggering the core is the best option.
Plywood Core Performance Factors
These 6 factors are things to consider with regard to the core type and how the overall panel will perform in use: