Early plywood began as a problem-solving exercise, because solid wood has issues.
Even when kiln-dried to a stable moisture content, treated, and painted, wood naturally wants to move when subjected to temperature and moisture changes and as it ages. In an environment built of many different pieces and maybe many different species, wood will struggle against itself, leading to warping, splitting, and popping joints.
By slicing logs into veneers, turning them 90 degrees against each other, and gluing them into a panel, you offset the natural stresses of wood and create a much more stable product. Generally, thicker veneers of lower-grade (less perfect) wood are used in the center. For furniture and architectural panels, face-grade decorative veneers are peeled from high-quality logs, which means fewer trees have to be harvested to create many more square feet of furniture and millwork surfaces with real wood.
Before we get into the most recent developments in core technology, a brief explanation of “softwoods” and “hardwoods” is necessary.
- “Hardwood” is the general term used to designate lumber or
veneer produced from trees that lose their leaves in cold weather, and produce seeds with a covering.
- “Softwood” is produced from trees that are usually needle-bearing
or coniferous, which keep their “leaves” year-round, and produce
seeds without a covering.
These terms do not indicate hardness in the physical sense: Balsa wood is very soft, but is considered a hardwood; bristlecone pine is quite hard, but is considered a softwood.
In choosing the best core for different applications, the main criteria are:
- Surface smoothness (compatible with your face veneer and
- Screw-holding strength
Different types of cores all carrying the same face veneer may be specified for different applications in a project as needed. Here’s a look at some of the most common options. (All weights listed are approximate, and for ¾-inch thick, 4- by 8-foot sheets.)
Particleboard: Very dimensionally stable and economical. It has a very smooth surface, reducing the risk of telegraphing through thin face veneers. Typically an engineered composition of recycled and recovered wood fiber meeting Eco-Certified Composite (ECC) panel requirements. Its consistent core improves edge profiling and machining characteristics. Requires edge treatment. Weighs 93 pounds.
CFC Veneer: Combination fiber cores (CFCs) have thin MDF crossbands (the layer just below the face veneer) over softwood veneer inner plies. The MDF provides an ultra-smooth surface to reduce telegraphing through the face, while the veneer inner plies maintain the strength and screw-holding power of a veneer core panel. This option is recommended for high-end veneers, as well as for transaction or writing surfaces because of the hardness of the MDF layers below the face veneer. Requires edge treatment. Weighs 75 pounds.
Multi-Ply: A premium-quality multi-layer veneer core panel constructed of nearly void-free, uniform birch veneer. This all-hardwood core produces an attractive, uniform edge for those requiring an exposed edge finish. Often used for drawer sides, this panel is also
preferred for its consistent cutting performance. Weighs 80 pounds.
MDF: Makes for a very smooth, consistent panel. This is a great substrate for high-end veneers and applications where routing and shaping are required. Weighs 100 pounds, the heaviest of
the core options.
Veneer: Constructed using inner plies composed of Western softwoods. Veneer core panels are lightweight, dimensionally stable, and have excellent screwholding capacity. Weighs 63 pounds, the lightest of the core options.
Hardwood Crossband Veneer: Combines the smooth finish of a hardwood veneer crossband beneath the face and back with the strength and durability of Western softwood veneer inner plies. Together they create an excellent hardwood plywood panel that is smoother and has less potential for core telegraphing. Weighs 65 pounds.
While most traditional wood glues are made with formaldehyde, some hardwood plywood suppliers offer core materials made with no-added urea formaldehyde (NAUF) adhesive systems. Many also use only Forest Stewardship Council (FSC) certified wood, as well as ECC particleboard and MDF.
Most materials on the market are also California Air Resources Board (CARB) Phase 2 compliant, and some manufacturers produce panels that
comply with CARB ATCM 93120 Ultra Low Emitting Formaldehyde (ULEF) Emission Limits, under Executive Order N-12-038.