What Is Plywood? Types, Grades and What to Use Where

Plywood is an engineered panel made from thin wood veneers glued together with the grain of each layer turned 90 degrees from the one below it, which makes a sheet flatter and harder to split than a solid board of the same thickness. The catch is that the stamp on the sheet matters more than the species: CDX, for example, is not an exterior panel. This guide explains how plywood is made, what the grade letters and span ratings mean, and how to match a type to your job.

What Is Plywood, and How Is It Made?

Plywood starts as logs peeled into continuous thin sheets of veneer. The veneer is dried, graded for defects, coated with adhesive, stacked with the grain direction alternating from layer to layer, and pressed under heat. According to APA, The Engineered Wood Association, structural panels are built with an odd number of layers so the panel stays balanced, then sanded or left rough depending on the grade.

A standard sheet is 4 feet by 8 feet, which is 32 square feet. The outer layers are called faces (or face and back), the layers between them are the core, and the thin layers with grain running across the sheet are called crossbands. Our guide to the 3-ply versus 4-ply tradeoff shows how layer count changes sanding and stability.

Why Cross-Grained Layers Beat a Solid Board

Wood swells and shrinks far more across the grain than along it. In a solid board that movement all goes one way, so the board cups or splits. In plywood each layer holds its neighbors in check, so the sheet stays flat and edge nails are less likely to split the panel.

The trade-off is direction. A panel is stiffest along the face grain, which is why span ratings assume the strength axis runs across the supports. When you cut a sheet for shelves, run the face grain along the span the shelf has to carry or it will sag sooner than the same shelf cut the other way.

Plywood Grades: What A, B, C and D Actually Mean

Each face veneer gets a letter. APA’s definitions are short, and they explain why a cheap sheet can have a rough back but still be structurally sound.

Veneer grade	What APA says	Where it makes sense
A	Smooth, paintable surface; the highest appearance quality	Visible cabinet faces, furniture, painted panels
B	Better appearance than C; limited repairs allowed	Shop projects where one face shows
C	The minimum grade for Exterior plywood; some defects acceptable	Sheathing, subfloors, hidden structure
D	Utility grade; limited to protected applications only	Back faces and inner plies inside a wall or floor

Sheets carry two letters, face first. An A-C sheet has one good face for the project and a rougher back you hide against a wall. Pair that logic with the BC versus Sande plywood breakdown, which separates the grade from the species, and with our look at which birch grade to buy for cabinets.

The CDX Myth: The X Does Not Mean Exterior

Many people read the X in CDX as exterior glue. APA states otherwise: CDX panels are Exposure 1, not Exterior. Exposure 1 is described as suitable for uses without long-term weather exposure, so the glue handles rain during construction, but a CDX sheet left outside for years will delaminate. Exterior panels are designed for repeated wetting and drying.

• Exposure 1: sheathing and subfloors that may get rained on before the roof goes on.
• Exterior: permanent outdoor use, with a C-grade or better face veneer.
• Marine: boats and docks, built with waterproof glue and a void-free core.

For the full comparison, read ACX versus CDX plywood, then check marine plywood versus pressure treated wood if the project will sit outside. If water is your worry, this page on wet OSB and plywood covers what happens to the edges.

How to Read Span Rating and Species Group Stamps

Structural panels carry a two-number span rating such as 32/16. The first number is the maximum spacing in inches between supports for roof use, and the second is the maximum for floor use, measured on center with the strength axis across the supports. So a 32/16 sheet can cover rafters 32 inches apart or floor joists 16 inches apart.

The species group is the other stamp. APA classifies more than 70 species under its PS 1 standard into groups, where Group 1 is the strongest and Groups 2 through 5 are progressively lower. Two sheets with the same nominal thickness can therefore be built from different species groups, so compare the stamp rather than assuming they perform alike.

Plywood Types by Core and Species

Type	Typical layers and species	Best for	Watch out for
Softwood plywood	Fir, pine or spruce veneers	Sheathing, subfloors, roofs	Rough face, possible patches and voids
Hardwood plywood	Oak, birch or maple face over a veneer core	Cabinets, furniture, shelving	Thin face veneer sands through easily
Baltic birch	Birch throughout, many thin plies, often metric thickness	Drawers, jigs, exposed edges	Often sold in 5 foot by 5 foot sheets
Marine plywood	Waterproof glue, void-free core	Boats, docks, wet areas	Costs several times more than CDX

For a head-to-head on one popular choice, see Baltic birch versus regular birch plywood. If you are weighing plywood against a panel made of fibers or strands, plywood versus MDF, CDX versus OSB, and chipboard versus MDF versus plywood each answer a different version of that question.

Sheet Sizes and Nominal Thickness

Plywood is sold by nominal thickness, and the real panel is often a hair thinner. A sheet sold as 3/4 inch is commonly about 23/32 inch, and a 1/2 inch sheet is commonly 15/32 inch. That gap matters for dado joints and for fitting into a rabbet cut with a 3/4 inch bit, which is why 15/32 versus 1/2 plywood and 1/2 versus 3/4 plywood are worth reading before you cut.

Standard stock sizes are 1/4, 1/2 and 3/4 inch for most 4 by 8 sheets, with 1/8 and 3/8 inch panels used for cabinet backs and underlayment. To budget the sheets, use the plywood price per square foot calculator or compare store pricing on Home Depot plywood prices.

Working With Plywood: Cutting, Joining and Finishing

Cutting Without Tearout

1. Score the cutline with a utility knife to sever the surface fibers.
2. Support the full sheet on a sacrificial foam board or scrap lumber so the offcut cannot pinch the blade.
3. Cut with the good face down on a circular saw and face up on a table saw.
4. Use a blade with 100 or more teeth on a 7-1/4 inch blade for any edge that will show.

Not every cut needs a power saw. Our page on cutting plywood with a hand saw covers thin panels, and plywood cut to size compares store cutting services with doing it yourself.

Joining and Edge Finishing

Screws hold well in the face but poorly in the edge, so plan butt, dado and rabbet joints with glue plus fasteners. How to join plywood together walks through each joint. Exposed plies can be hidden with veneer edge banding, and sealing the edges matters most of all because edge grain is where moisture gets in. Before painting, read how to paint plywood so the grain does not telegraph through.

Formaldehyde, Dust and Indoor Use

Plywood glues can release formaldehyde. Under the EPA’s TSCA Title VI rule, hardwood plywood with a veneer core is limited to 0.05 ppm, matching the California Phase 2 level, and no-added-formaldehyde and ultra-low-emitting resins have separate certification paths. Panels made with phenol-formaldehyde glue emit less than those made with urea-formaldehyde glue. For bedroom furniture and kitchen cabinets, ask for the compliance label.

Sawdust is a separate issue. Cutting and sanding plywood throws fine dust that contains wood and resin, so wear an N95 or better mask, cut outdoors or with dust collection, and keep a shop vacuum on the saw.

Storing and Maintaining Plywood

Store sheets flat on evenly spaced supports, or stand them nearly upright with the whole edge supported. A sheet leaned at a steep angle for weeks can take a permanent bow. Keep panels off bare concrete, which wicks moisture upward, and out of direct sun. Let a sheet acclimate in the room for a few days before cutting furniture parts, and check the edges for lines that signal separation.

Frequently Asked Questions

What are the different grades of plywood?

Plywood veneers are graded A through D. A is smooth and paintable, B allows limited repairs, C is the minimum for Exterior panels and may carry knots and patches, and D is a utility grade for protected uses only. A sheet is labeled with two letters, one for the face and one for the back, such as A-C.

Is CDX plywood exterior grade?

No. According to APA, CDX panels are Exposure 1, not Exterior. Exposure 1 glue survives construction delays and rain during building, but it is not meant for long-term weather exposure. For a deck, boat or permanent outdoor use, buy panels stamped Exterior or true marine plywood.

What does 32/16 mean on a plywood stamp?

It is the span rating. The first number is the maximum support spacing in inches for roof use and the second is the maximum for floor use, with the panel’s strength axis running across the supports. A 32/16 panel can span rafters 32 inches apart or floor joists 16 inches apart.

Why does plywood have an odd number of layers?

Odd-ply construction puts the same grain direction on both faces and around a center layer, which balances the panel so it stays flat and carries similar strength on each side of the core. Some multi-layer panels, such as certain Baltic birch sheets, are built differently, so check the product spec.

Is plywood stronger than solid wood?

As a flat panel, plywood resists splitting and warping better than a solid board of the same thickness because adjacent layers run at right angles. Solid lumber is still the better choice for framing members like studs and joists, where the grain should run the full length of the part.

Is plywood safe to use indoors?

Interior hardwood plywood sold in the United States must meet the federal formaldehyde emission limit of 0.05 ppm for veneer-core panels under TSCA Title VI. Look for a compliance label, seal cut edges on furniture, and wear a dust mask when cutting or sanding because the dust contains wood fiber and resin.

Conclusion

Plywood works because the layers cancel each other’s movement, but the stamp tells you whether a sheet fits the job. Read the veneer grade for appearance, the Exposure or Exterior rating for moisture, and the span rating for structure, and ignore the idea that CDX means exterior. Match those three to where the panel will live, and you will pay for exactly the sheet you need.