Plywood grades and cores: choosing sheet goods

Plywood is layers of wood veneer glued with the grain of each layer crossing the one below. The cross-lamination is what makes it stable in both directions and why it can be glued or screwed without allowing for seasonal movement. But “plywood” covers sheets as different as a rough construction panel and a void-free birch sheet for drawer boxes. The core and the grade decide which one you have.

Cores

Core	Strengths	Weaknesses	Typical use
Veneer core	Light, stiff, holds screws in its edge reasonably well	Can have voids; faces can telegraph the plies beneath	Cabinet cases, shelves
MDF core	Very flat, smooth, consistent thickness	Heavy; poor screw holding in the edge; swells if wet	Painted work, doors, panels that must stay flat
Combination core	Veneer inner plies with MDF layers under the faces: flatter than veneer core, lighter than MDF core	Costs more than veneer core	Quality cabinets
Particleboard core	Inexpensive, flat	Heavy, weak edges and fasteners	Budget casework, countertops under laminate
Baltic birch	All-birch plies, more of them, few voids, attractive edge	Often metric thickness, often 5 × 5 ft sheets	Drawer boxes, jigs, exposed-edge work

Hardwood plywood, with a cherry, oak or maple face, is usually veneer core, MDF core or combination core. Ask which you are buying; the face looks the same.

Reading grades

Hardwood plywood in North America is graded with a letter for the face and a number for the back:

• Face grades run from AA and A (best, with few, well-matched veneer pieces) through B, C and D (more patches and colour variation).
• Back grades run from 1 (sound, few defects) to 4 (open defects allowed).
• So “A-1” is a premium sheet with a good back, while “B-2” or “C-3” costs less and suits parts where one face is hidden.

Softwood construction plywood uses letters for both faces, A through D, with the face first: “CDX” is a C face, D back, and glue rated for exposure during construction. Exposure-rated glue does not make the panel suitable for weather.

Baltic birch uses its own grades, most commonly B/BB: a clean face and a back with colour-matched patches. CP and C grades allow more patches and are sold for utility work.

Grading rules and their names vary by country and mill. Look at the actual sheets before buying for show surfaces.

Thickness

Plywood is almost never as thick as its label. A “3/4-inch” sheet is often 23/32 inch, and Baltic birch is metric (18 mm is 0.709 inch). Measure every sheet before sizing dadoes and rabbets; see nominal and actual sizes and dadoes and rabbets in plywood.

Which sheet for which job

• Stained or clear-finished cabinets: hardwood plywood, veneer or combination core, A or B face on the show side.
• Painted cabinets and doors: MDF or MDF-core plywood. It paints without grain showing through and stays flat.
• Drawer boxes and exposed edges: Baltic birch, finished with the edge showing.
• Shop furniture and jigs: Baltic birch for durable jigs; sanded softwood plywood for benches and storage.
• Case backs and drawer bottoms: 1/4-inch hardwood plywood, measured before cutting grooves.

Edges

The edges of most plywood show the plies and voids. Cover them with iron-on edge banding, a thin strip of solid wood glued on, or a thicker solid edge that also stiffens a shelf. Plan the edging in the cut list, since it changes the size of the panel you cut.

Handling and storage

Store sheets flat or on edge fully supported; a sheet leaned at an angle for weeks will bow. Let sheets acclimate in the shop before cutting. Break full sheets down with a track saw or circular saw into manageable pieces before final cuts; see planning a cut list.

In GrainDraft

GrainDraft’s sheet layout arranges plywood and MDF parts on quarter, half or full sheets with your saw kerf between them and prints a pencil-marking PDF measured from a datum corner. Give sheet parts their measured thickness so joints fit the stock, and use face-grain direction in the model to keep visible parts consistent.

Related: choosing a wood species, board feet.