Packaging guide
3-ply, 5-ply or 7-ply
What the ply number counts, roughly how much weight each construction carries, and how to choose without paying for board you do not need.
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In short
- Ply counts the layers of paper. 3-ply has two liners and one fluted medium; 5-ply has three liners and two mediums; 7-ply has four liners and three mediums.
- As a rough guide, 3-ply carries about 4–15 kg, 5-ply about 20–45 kg, and 7-ply above that.
- Those figures are typical, not guaranteed — board grade, box size, stacking height and humidity all move them.
- Ply is only half of a specification. The paper grade, quoted as GSM and BF, is the other half.
- The right choice is the lightest board that protects the product for the journey it actually makes.
What the number counts
Ply counts layers of paper, not layers of cardboard. A corrugated board is built by gluing a wavy fluted sheet between flat liner sheets, and the ply number is the total of both kinds.
So 3-ply is a liner, a flute and a liner — three sheets. Adding a second flute and a third liner makes 5-ply. A third flute and fourth liner makes 7-ply. The trade also calls these single wall, double wall and triple wall, which mean exactly the same thing.
3-ply
Single wall
Two liners with one fluted medium between them.
4–15 kgtypical load
Retail cartons, e-commerce and courier boxes, inner packs, light to medium goods.
5-ply
Double wall
Three liners with two fluted mediums between them.
20–45 kgtypical load
Heavier goods, stacked storage, longer road journeys, ration and bulk packs.
7-ply
Triple wall
Four liners with three fluted mediums between them.
Above 45 kgtypical load
Industrial loads, machinery parts and export cartons, often in place of a wooden crate.
Roughly how much each carries
These are typical ranges, not guarantees. They are a starting point for a conversation, and any carton we quote is specified against your actual load rather than against a table.
| Construction | Also called | Typical load | Commonly used for |
|---|---|---|---|
| 3-ply | Single wall | 4–15 kg | Retail, e-commerce, courier, inner packs |
| 5-ply | Double wall | 20–45 kg | Heavier goods, stacking, ration and bulk packs |
| 7-ply | Triple wall | 45 kg and above | Industrial, machinery, export in place of a crate |
What moves those numbers
Two cartons of the same ply can perform very differently. Four things account for most of the gap:
- Board grade. The GSM and BF of the papers used. This is the biggest single factor after ply, and it is covered in GSM and BF explained.
- Box size. A large panel flexes more than a small one under the same load, so a big box needs more board than a small box carrying the same weight.
- Stacking height and time. Board loses compression strength the longer it is held under load. A carton that is fine on a truck can fail in a warehouse after weeks at the bottom of a stack.
- Humidity. Corrugated board weakens as it absorbs moisture. A monsoon warehouse or a shipping container is a harder environment than an air-conditioned store room.
How to choose
The rule is simple and it saves money in both directions: the right specification is the lightest board that protects the product properly for the journey it actually makes.
Over-specifying is the more common mistake. Moving a job from 3-ply to 5-ply because it “feels safer” adds cost to every single carton for the life of the product. Under-specifying is rarer but more expensive when it happens, because the loss is the goods rather than the box.
In practice, describe three things and the answer follows: what the product weighs, how the cartons are stacked and stored, and how far they travel and by what route.
Where to go next
- GSM and BF explained — the paper grade half of a specification.
- Corrugated cartons — what we make in each ply.
- Cartons for safety matches — a light load where the stack, not the weight, decides the ply.
- Corrugated sheets — the same board supplied flat.
Common questions
What does ply mean on a carton?
Ply counts the layers of paper in the board. A 3-ply board has three: an outer liner, a fluted medium, and an inner liner. A 5-ply board has five — three liners with two fluted mediums between them — and a 7-ply board has seven. More layers mean more strength, more thickness and more cost.
How much weight can a 5-ply box hold?
Typically in the range of 20 to 45 kg, though that is guidance rather than a guarantee. Actual capacity depends on the paper grade used, the size of the box, how high it is stacked, how long it is stored and how humid the conditions are. A 5-ply carton in a good board grade will outperform a 5-ply carton in a poor one.
Is 7-ply always better than 5-ply?
Not for most jobs. 7-ply costs more, weighs more and takes more space flat, so specifying it for a load that 5-ply carries comfortably is money spent on nothing. The right specification is the lightest board that protects the product properly for the journey it makes.
What is the difference between single wall and double wall?
They are the same thing as 3-ply and 5-ply. Single wall means one fluted layer between two liners; double wall means two fluted layers with a liner between and either side. Triple wall, or 7-ply, has three.
Does ply alone decide how strong my box is?
No. Ply describes the construction; the paper grade describes the material. A carton is specified by both — the number of plies and the GSM and BF of the papers used. Two 5-ply cartons can differ substantially in strength if their board grades differ.
Which ply should I use for export?
Export cartons are usually 5-ply or 7-ply, because they face longer journeys, more handling and higher stacks in a container. Where a wooden crate would once have been used, a 7-ply carton is often lighter, cheaper and easier to handle. Describe the shipment and we will suggest a specification.
