What plywood is
The Wood Handbook defines plywood as a panel built from sheets of veneer, called plies, laid with the grain of each layer at right angles to the next and always with an odd number of layers. The outside plies are the face and back; inner plies running the same way as the faces are centers, and those running across are crossbands. That construction gives plywood its working qualities: strength along and across the sheet, dimensional stability in both its length and width, little permanent thickness swelling if it gets wet, and — because the crossed layers resist splitting — the ability to take fasteners close to its edges.
Two kinds of plywood
| Feature | Construction and industrial | Hardwood and decorative |
|---|---|---|
| Standard | PS 1 (and PS 2 for performance) | ANSI/HPVA HP-1 |
| Graded by | Veneer quality of face and back (letters), use, exposure | Species and face veneer, bond durability, center construction |
| Woods | Mostly softwoods: Douglas-fir, southern yellow pine, true firs, hemlock, western pines | Many species, domestic and imported; well over half of panels used in the US are imported |
| Exposure | Exposure 1 or Exterior; all now boil-proof bonded | Interior or Exterior |
| Labelled thickness | Performance Category, with a thickness range | Nominal; measure the sheet |
| Typical use | Sheathing, subfloor, shop jigs, painted work | Furniture, cabinets, paneling; a substantial portion sold prefinished |
From the Wood Handbook, Chapter 11; Performance Category ranges are on the plywood thickness chart.
Softwood face grades and sanded plywood
| Grade | Boise Cascade's description |
|---|---|
| A | Smoothest, no knots, nearly free from defects; paintable; used in cabinets and furniture where appearance matters |
| B | Like A but with more repairs, some up to 1 in across; tight knots permitted |
| C-plugged | An improved C veneer with some minor defects |
| C | Unsanded, several minor defects, knots up to 1-1/2 in across |
| D | Defects not repaired; knotholes up to 3 in wide within limits; a limited number of splits |
Boise Cascade's own wording. Panels are named face then back: an AC panel has an A face and a C back. Other makers and the PS 1 standard set the exact limits; check the stamp.
'Sanded plywood' in a lumber yard usually means a panel like Boise Cascade's: a multilayer softwood core sanded on both sides, sold as AC (A face, C back) or BC (B face, C back) from 15/32 to 1 in thick. It is meant for cabinetry and furniture where the face shows, and is paintable, in the maker's word; for a clear finish or stain, hardwood plywood's face veneers are selected for appearance instead. A C or D face, by the same maker's descriptions, is unsanded or allows open knotholes: a sheathing face, not a show face.
Hardwood plywood cores
| Core | Weight, 3/4 in panel | What Columbia says about it |
|---|---|---|
| Veneer core | About 70 lb | Lightest; best spanning strength; wider thickness variance; can telegraph through thin faces |
| Combi-core | Not given | Veneer inner plies with MDF or particleboard crossbands: veneer-core strength with a void-free surface |
| MDF core | Around 100 lb | Most stable with temperature and humidity; smooth, void-free; better screw holding than particleboard |
| Particleboard core | Up to 100 lb | Very uniform thickness; least spanning strength; swells most if wet |
| Multi-ply birch | About 85 lb (Europly PLUS) | High ply count, all hardwood; for work where the edge shows |
Columbia Forest Products' core guide, for its own panels. A shelf that must span favours veneer core; a flat painted door panel favours MDF.
Hardwood plywood is also commonly sold completely finished — prefinished — which saves finishing inside cabinets. Stainable panels are those with real wood faces; the face is thin, so sand lightly and test the stain on an offcut, as veneer explains. Overlaid and coated panels, such as those made for concrete forms, are special grades for their use, not furniture stock.
MDF, particleboard and OSB
- MDF is made from wood fibres and adhesive pressed into a smooth, uniform panel; the Handbook notes its use in place of solid wood, plywood and particleboard in furniture, and for mouldings and trim. It is classified under ANSI A208.2.
- Particleboard is made from small wood particles bonded under heat and pressure, usually in three layers with fine particles at the faces for a smooth surface for laminates and veneers (ANSI A208.1).
- OSB is made from long strands in layers oriented like plywood's, for sheathing and subfloors; it is a construction panel, not a furniture face.
- Compared on screws and span, Columbia rates MDF above particleboard for screw holding and veneer core above both for spanning.
Choosing a sheet for the job
| Work | A sheet that suits | Why |
|---|---|---|
| Shop jigs, templates | Sanded softwood or MDF | Flat and stable; MDF smooth and void-free |
| Painted cabinets and shelves | AC or BC sanded plywood, or MDF-core | A smooth face; MDF core for flatness |
| Clear-finished cabinets and furniture | Hardwood plywood, veneer or combi-core | Selected face veneer; combi-core avoids telegraphing |
| Exposed edges, drawer boxes | Multi-ply birch | Made for work where the edge shows |
| Shelves that span | Veneer-core plywood | Best spanning strength of the cores compared |
| Anything left wet | Exterior-rated panels | The bond class sets the exposure, not the face |
Built from the Handbook's and the makers' statements above; no span table is given, because none of the documents reviewed gives one for furniture shelves.
Before buying plywood
- Construction or hardwood plywood, by the finish you plan
- Face and back grade, read from the stamp
- Core chosen for span, weight and edge
- Actual thickness measured, not read from the label
- Interior or exterior bond for where it will live
- Sheets counted with the plywood calculator
The rest of this series
- Veneer: how face veneer is cut, how thick it is, and why it sands through.
- Working with plywood: breaking down sheets, clean edges and circles, joints sized to the sheet, edge banding and fastening.
- Utilities: the plywood calculator counts sheets, the cut list optimizer lays parts out on them, and the plywood thickness chart gives what a sheet measures.
- Solid wood, for edging and frames: choosing lumber.
Sources
Grades and cores are described by the makers named, for their own panels; other makers' products differ. The hardwood plywood standard ANSI/HPVA HP-1 was not reviewed directly, so its face-grade letters are not given here.
- 1.
Chapter 11: Wood-Based Composite Materials: Panel Products, Glued Laminated Timber, Structural Composite Lumber, and Wood–Nonwood Composites. USDA Forest Service, Forest Products Laboratory — Wood Handbook, FPL-GTR-282, 2021.
Used for: Plywood as plies of veneer with adjacent layers at right angles and always an odd number of layers; faces, backs, centers and crossbands; strength along and across the panel, dimensional stability along its length and width, minimal irreversible thickness swelling, fasteners near edges without splitting; solid-core panels for small pieces; the two classes — construction and industrial (PS 1; Exposure 1 and Exterior; mostly softwood; PF adhesive) and hardwood and decorative (ANSI/HPVA HP-1; species and face veneer; veneer, lumber, particleboard, MDF or hardboard centers; Interior and Exterior; much of it imported; a substantial portion sold finished); grade stamps with Performance Category and thickness label; special grades such as concrete-form panels; particleboard, MDF (ANSI A208.1 and A208.2) and OSB.
- 2.
Plywood — veneer grades. Boise Cascade.
Used for: A panel maker's face and back veneer grades: A smoothest, paintable, no knots; B with repairs up to 1 in and tight knots; C-plugged; C unsanded with knots up to 1-1/2 in; D with unrepaired defects and knotholes up to 3 in; panels named by two letters, face then back.
- 3.
Sanded Plywood. Boise Cascade.
Used for: A sanded softwood plywood: multilayer softwood core, sanded both sides; AC (A face, C back) and BC (B face, C back); 15/32 to 1 in; 4 × 8 ft; western species; for cabinetry and furniture where appearance matters.
- 4.
Hardwood Plywood Core Guide (as hosted by a distributor). Columbia Forest Products.
Used for: A hardwood plywood maker's cores: veneer core (about 70 lb per 3/4 in panel; best spanning; wider thickness variance; core can telegraph through thin faces, two-step builds recommended for high-end plain-sliced faces); combi-core (veneer inner plies with MDF or particleboard crossbands); MDF (around 100 lb; most stable; smooth; better screw holding than particleboard); particleboard (up to 100 lb; least spanning strength; greatest expansion when wet); multi-ply birch for exposed edges (Europly PLUS about 85 lb).
- 5.
Panel Thickness Tolerances and Labeling (Technical Topic TT-054). APA — The Engineered Wood Association, 2013.
Used for: Structural panels labelled by Performance Category and thickness rather than nominal thickness alone.
- 6.
What is the PS2 Performance Category? (HUB 9114), quoting PS 2-10, Table 1. Huber Engineered Woods, 2018.
Used for: Performance Category thickness ranges under PS 2-10.
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