Plywood Types

Plywood Types and Application

Originally, “plywood” referred only to wood panels made of multi-layered veneer, laid with the grain perpendicular to adjacent layers, and bonded together with glue. While this term is still accurate, the name plywood has expanded, becoming more generic today. It now refers to all engineered wood panels, regardless of their form or manufacturing process. The list of these can seem endless. Nevertheless, we can break down the various types of plywood into some basic categories.

Plywood is graded in many ways, specifically by the type of face veneer it has and the way it is manufactured. When looking at plywood for a project, one of the first things considered after selecting the type of plywood product is the grade or quality of the face veneer the plywood is made with. There are four letter grades for these veneers:

Grade	Definition
A	A smooth, paintable surface, containing no more than 18 neatly made repairs, which don’t affect the overall smoothness of the surface. Repairs must be made in the direction of the grain.
B	Solid surface, with no voids. Shims, routed repairs and knots up to 1 inch across are allowed. Repairs and patches can be made of wood or synthetic materials. Some minor splits are allowed.
C	Tight knots up to 1 ½ inch and knotholes up to 1 inch are allowed. Discoloration and sanding defects are allowed, as long as they do not affect the strength of the panel. Discoloration is also allowed. Limited splits are permitted.
D	Can contain knots and knotholes up to 2 ½ inches limited splits are allowed. Limited to use as interior panels, or the inner side of exterior panels.

Important Plywood Terms to Know

As with many other things, working with plywood means dealing with some special vocabulary. You may not know these terms if you’re new to woodworking or working with plywood. Without them, you won’t necessarily know what you’re dealing with.

• Back – plywood side with the lower face grade, normally used as the back, when installed
• Core – inner layers of the plywood, with the grain perpendicular to the face
• Crossbar – manufacturing defect where a piece of face veneer runs perpendicular to the board’s length
• Crossbanding – orientation of successive veneer layers, placing them perpendicular to the adjacent layers of the plywood
• Cut – refers to how the veneer is made, either rotary cut or sliced
• Delamination – failure of plywood panels, where the adhesive used to attach the fails, usually due to water
• Face – the side of the plywood with the higher grade finish
• Grade – system by which the quality of plywood’s surfaces is identified
• Grain–growth pattern of wood fibers
• Gum Spots – sap or resin leftover on wood veneer from milling
• Hardwood – any wood that comes from a deciduous tree (one whose leaves fall off) – has nothing to do with the wood’s density
• Heatwood – the center of the log, below the sapwood; also the strongest part of the log
• Knot – place on a log where a branch grew out
  • Open Knot – the knot has separated from the wood around it, leaving a hole
  • Pin Knot – small knots, less than ¼” in diameter
  • Sound Knot – a knot that has not separated from the wood surrounding it
• Knothole – a hole or void in lumber where a knot has come out
• Lap – a place where two pieces of veneer are laid next to each other on the same ply
• Marine Plywood – high-quality plywood made with waterproof glue and without any voids
• MDF (Medium Density Fiberboard) – engineered plywood product made of highly compressed, pressure-cooked wood fibers combined with synthetic resin
• Mineral Streak – discoloration of hardwood
• Oxidation – browning, graying, or yellowing caused by exposure to the elements
• Particleboard – engineered wood product manufactured from small wood particles (sawdust) with a bonding resin – is not the same as MDF, which is a higher-grade product
• Patches – material placed on defects in face veneers to repair voids, etc.
• Ply – a single layer of wood veneer in a plywood product
• Plywood – originally referred to as an engineered wood product, made by laminating several wood veneer perpendicular to each other. The definition has now been expanded to include all engineered wood sheet products
• Rotary Cut – the process by which veneer is peeled off a log as one continuous sheet on a lathe
• Sapwood – outer layers of living wood, just below the bark; normally not used in plywood
• Splits – cracks in the wood veneer, running parallel to the wood grain
• Veneer – sliced or peeled a layer of thin wood used to make plywood

Here are the most common types of plywood currently available on the market.

Softwood Plywood

This is the most common plywood product, made of softwood veneer, usually fir. By “softwood,” we refer to woods that come from various conifer trees rather than broadleaf trees. Softwood plywood is commonly used for construction applications because these trees grow throughout the year, allowing the tree to reach full stature much more quicker. This also makes softwoods less expensive, which translates to lower-cost plywood products.

Softwood plywood was originally developed for the construction industry, although it is used in various other applications. It is the prime choice where the durability of a multi-layer plywood product is needed, but a fine surface finish is not.

In manufacturing, an odd number of layers of softwood veneer are stacked at a right angle to each other and glued together with resinous glues to form softwood plywood. This plywood sold in the United States usually comes in 4’ x 8’ sheets, although 5’ x 5’ sheets are also available. A large number of grades are available, depending upon the intended application. Please see the page on CDX plywood for a more thorough explanation of the grading system.

Softwood plywood is used most commonly in the building trades for wall and roof sheathing and installation as sub-floors. It is also commonly used to construct crates and boxes to ship expensive, delicate, or heavy machinery. Due to its availability, softwood plywood is an excellent choice for homebuilding and do-it-yourselfers.

This is the plywood you will most likely encounter when visiting the local lumberyard or home improvement center. While they will have some other plywood products, most will be softwood.

Hardwood Plywood

This group of plywood products covers many materials, including plywood made with decorative face veneer from any hardwood tree. In practical terms, there are only a few common hardwood plywood types. All other types of wood grain are simulated by staining common hardwood plywood panels.

Hardwood plywood is manufactured like softwood, except the exterior layers (face and reverse) are made of a thin hardwood veneer. This veneer is usually thinner than the face and reverses the face veneer used to manufacture softwood plywood. In any case, the core layers are typically softwood to help control cost. You can also find lumber core hardwood plywood, which has a single core layer of strips of wood laminated together, much like a butcher block.

This plywood category is most commonly used for cabinet and furniture making, where a smooth, attractive surface is required for finishing. Common hardwood plywood includes ash, red oak, birch, maple, and mahogany. It is typically AB grade plywood, meaning the face side is A grade, and the reverse face, which becomes the inside of the cabinet, is a B grade.

Contrary to what I just said, the backs of hardwood plywood are not graded in the same way that the backs of other types of plywood are. A separate grading system is used to give a better understanding of how the two faces of the plywood match up for cabinet and furniture making:

1. Sound, same species, specifically cut
2. Solid, same species, specifically cut
3. Rotary Grain
4. Reject Back

Cabinet Grade Plywood

Essentially cabinet grade plywood is the same as Hardwood plywood, but some people prefer this term. Generally speaking, cabinet grade plywood refers to ash and birch hardwood plywood. This term does not refer to the other types of hardwood plywood.

Lumber Core Plywood

This is a sub-category of hardwood plywood. However, this product is not very common and is reducing in popularity. Nevertheless, you can still find it used in cases where the plywood edges cannot be concealed by other wood trim or need to be routed.

Typically, lumber core plywood is three-ply plywood, the outer veneers being hardwood and the inner layer being lumber core, made of several strips of solid lumber, typically basswood. Those strips are bonded together and bonded to the face veneers. The result is a plywood product that meets a particular need but is not as strong as most others.

When selecting lumber core plywood, take care to ensure that there are no voids in the core. Unlike marine grade plywood, there is no guarantee that there will not be any voids.

Marine Plywood

Marine plywood is a special softwood or hardwood plywood designed for use in the construction of boats but used for other applications, especially when some moisture resistance is needed. It is specially treated to resist rotting in high-moisture environments. But the main characteristic which separates marine plywood from all other types is that marine plywood is manufactured with no “voids” – the gaps in the core layers caused by splits or knotholes. This prevents water from becoming trapped in those voids.

Most marine plywood is also graded as Water Boiled Proof (WBP), a rating that refers to the glue used in bonding the layers of veneer together. In this case, the glue is similar to what is used on exterior plywood to bond the layers. The rating indicates that test panels of this plywood material have been subject to being boiled in water to determine if they will delaminate. The combination of heat and moisture is hard on adhesives, tending to soften them.

The combination of features contained in marine plywood greatly affects the price. Marine plywood costs about three times the cost of standard plywood.

Aircraft Plywood

Aircraft plywood or “airplane plywood” was in common use in the construction of airplanes in World War II. It is a thin birch or hardwood plywood (mahogany, beech, walnut, and Douglas fir have all been used) and can be considered the highest quality plywood product made, even better than marine plywood.

Like marine plywood, aircraft plywood requires that the core veneers are void free, with no knotholes or splits. Face and reverse face veneers are allowed to contain tiny, closed knots. Due to their use, they come in much larger sheets to provide a continuous surface for covering wings. Typical thicknesses range from 1.2mm to 5mm.

Overlaid Plywood

Overlaid plywood is a specialty used primarily to manufacture concrete forms, although it has found a home in other industrial applications, such as containers. It is manufactured similarly to softwood plywood, except for the outer face layers. Those are made to be smooth and durable, usually resin-impregnated fibers.

Phenolic board or phenolic plywood is similar to overlaid plywood in its manufacture and result. The main difference is that this plywood has been made specifically for use in the building of concrete forms. It comes in two grades: HDO (high-density overlaid) and MDO (medium-density overlaid). Each of these is available in a concrete grade and a general grade. HDO leaves a smooth “steel-form” finish on the concrete, while MDO leaves a matte finish.

Particle Board

Particle board, often called “chipboard,” is made of sawdust, shavings, and tiny pieces of wood, mixed with glue, and pressed into sheets. It is the most economical but the weakest of all plywood products. Particle board is commonly used under laminates on countertops and for shelving. Most inexpensive furniture uses vinyl-covered particle board for large surfaces, usually trimmed with solid wood.

Due to the high rosin content in this product, it tends to be heavier than other plywood products. Nevertheless, the low cost makes it extremely popular. Particle board should not be used in any application which requires structural strength or which will be subject to any sort of impact. Nor is normal particle board moisture resistant in any way. Left outdoors in the rain, this product soaks up water rapidly, expanding the thickness while ruining what structural integrity it does have.

There is a moisture-resistant particle board, often called “green chipboard.” This uses a different rosin, which is much more water-resistant. This allows the core of the board to retain its dimensional stability, even when the surface of it, which does not use this type of rosin, does not.

Medium Density Fiberboard (MDF)

MDF differs from Particle Board because it is created from wood fibers instead of sawdust and wood chips. This creates an extremely flat board (flatter than softwood plywood made from veneers) consistent in material thickness and density, with no voids. Due to its very smooth finish, MDF is excellent for painting or vinyl veneer coating. MDF is slightly stronger than Particle Board and is taking over the furniture market from the latter. It has the greatest weight when compared to other types.

Tempered Hardboard

More properly known as “high-density fiberboard” (HDF) and commonly referred to by the trade name “Masonite.” Tempered hardboard is an engineered wood product, much like MDF. The difference comes from the manufacturing process, specifically how the wood fibers are harvested from the wood. This difference in the process allows the wood fibers to be pressed much tighter together, making a denser product, with a density between 65 lbs/ft³ and 90.5 lbs/ft³.

Tempered hardboard is only produced as thin, between 1/8” and ¼” thick. One of the most common uses is pegboard, where perforations are made in a grid, allowing hooks to be inserted for hanging tools or merchandise on the board. The non-perforated version of this product is used extensively in skate parks to make skateboard ramps and half pipes. It’s natural flexibility and hard surface lend to this sort of application.

Oriented Strandboard (OSB)

While most people consider OSB inferior to plywood, building codes recognize it as an equivalent material, especially for roof and wall sheathing. Instead of wood veneers, OSB is manufactured from wood chips or strands, creating about 50 layers in the average sheet, compared to 5 or 7 in softwood plywood. It costs about 20 to 30 percent less than a comparable thickness sheet of softwood plywood. OSB is commonly used in construction for sheathing, roof decking, and subflooring. It is available in sheets up to 24 feet long.

While OSB can support as much weight as plywood, making it meet building code, it is not as resistant to impact as plywood is. In testing to break a strip of OSB by striking it with a hammer, it will break much easier than a comparable thickness of softwood plywood.

Baltic Birch

Otherwise known as “Russian Birch,” is a plywood material imported from Russia, hence the name. It differs from domestic plywood in that it has a much higher number of plays (9 for 1/2” and 13 for 3/4”), making it very attractive for drawer sides and modern furniture applications. It is commonly used in applications with bullnose edges, where solid wood edging cannot be installed. Because it is manufactured to a different standard, Baltic Birch normally comes in 5’ x 5’ sheets, although 4’ x 8’ are becoming more common. When looking at the price, Birch is the most expensive type of plywood on the market.

ApplePly

This plywood product, like Baltic Birch, is manufactured from more layers than standard softwood or hardwood plywood. It is made from uniform laminations of solid 1/16” Alder and Birch, both low-density hardwoods. There are a minimal number of voids, and the high number of laminations provides an attractive edge for furniture and cabinetry, which machines extremely well. ApplePly is available in thickness ranging from 1/4” through 1-1/4” in sheets up to 10’ long.

Foam Board

A recent addition to the plywood family is foam board. This composite material consists of a polyurethane foam core with wood faces; generally, a thin plywood product can include Lauan plywood, MDF (medium density fiberboard, and others. The core may be reinforced with fiberglass, producing a finished product as strong as softwood plywood.

The benefits of foam board over other plywood products are the lighter weight and rot resistance. Being made with a non-organic core eliminates the ability of bacteria or insects to damage the product. The foam core also provides some insulating value, which is not found in other plywood products. The lighter weight makes it easier to install.

Due to the foam core, this product is normally installed with adhesives rather than fasteners. Nailing the boards, for example, would tend to crush the foam board, and a miss with a hammer could put a hole in it.

Bending Plywood

Another new plywood product is bending plywood. As its name indicates, this product has been designed for projects requiring curved surfaces. More than one type of bending plywood is made, so selecting the right one for the building project is necessary.

• Bending plywood can be made to bend cross grain or long grain
• Bending plywood can be two-ply, with a single veneer face, or three-ply with two veneer faces. The veneer faces are equal; there is no face and reverse face
• These plywood products are normally quite thin: 1/8”, 1/4”, 3/8” and their metric equivalents

These products are mostly designed for architectural work, making cabinets and columns. However, they can be used for cabinets and furniture making as well. They are designed for a minimum 12-inch radius. While it may be possible to bend them into a tighter radius than that, special equipment and methods may be required. As a general rule of thumb, you don’t want to curve it any tighter than you can push the wood by hand.

Luan, Oak, Cedar, Maple, Phenolic, Spruce, Pine, Cherry, MDO, and HDO plywood are described in detail on a separate page.