Corrugated board is a wavy layer of paper, called the flute, glued between flat sheets called liners. The flute letter tells you how thick the board is, and the number of walls tells you how strong it is. Pick the lightest construction that survives your product's journey, because extra board costs money on every piece and every shipment.
Updated 20 October 2026 · By the EasyPak team in Qormi, Malta
Buyers often ask for "strong boxes" and leave the rest to the supplier. That works, but you will get a better price and fewer damaged parcels if you understand the three choices underneath: the flute, the number of walls, and the paper used for the liners.
A single-face board is one fluted layer glued to one flat liner. Add a second liner on the other side and you have single-wall board, the standard material for most shipping boxes. Two fluted layers with three liners make double-wall board, used for heavier products and for boxes that sit at the bottom of a tall pallet stack. Triple wall exists for very heavy industrial loads.
Flutes are named by letter. The letters are historical, so they are not in size order, which confuses almost everyone the first time. The thicknesses below are typical published values; actual board varies a little by mill.
| Flute | Typical thickness | Where it is used |
|---|---|---|
| A flute | about 4.8 mm | Cushioning for fragile goods; less common today |
| C flute | about 4.0 mm | General shipping cartons with good stacking strength |
| B flute | about 3.2 mm | Smaller shipping boxes, good puncture resistance and print surface |
| E flute | about 1.6 mm | Mailers and retail boxes, takes print well, folds neatly |
| F flute | about 0.8 mm | Very thin, close to a carton feel, for small retail packs |
Double-wall boards combine two flutes, for example B and C together, which gives the stacking strength of a thicker board while keeping a reasonable outside surface for print.
Two measures come up when suppliers talk about strength. Edge crush tests how much load the board can take on its edge before it buckles, which matters for stacking. Box compression tests a finished, empty box under a press, which tells you how much weight a stack can carry. If your cartons sit on pallets for weeks in a warm warehouse, ask about compression strength. If they travel by courier, puncture resistance and a well-fitting insert often matter more.
The liners can be made from recycled fibre or from virgin fibre, often called kraft. Recycled liners are the sensible default for most shipping boxes and keep cost down. Virgin kraft liners are stronger for the same weight and resist moisture better, so they earn their place on heavy loads, export journeys and cold-chain products. Recycled and recycled-content board is our standard starting point, with FSC-certified board available where your procurement or reporting rules ask for it.
Folding cartons are made from paperboard, not corrugated board. Under ISO terminology, paperboard is generally paper heavier than 250 grams per square metre. The common grades are:
Thickness and stiffness matter more than the name. Ask for a physical sample, fold it, and hold it with your product inside. That tells you more than any data sheet.
We start from the product's weight, its fragility, how it travels and how long it sits in storage. Then we pick the lightest board that does the job, because every extra gram is paid for twice: in the board and in the freight. The choice is proved on a physical sample before any full run. If you would rather tell us the conditions than choose the board yourself, the spec builder lets you leave the material as "recommend for me".
What is the difference between single wall and double wall?
Single-wall board has one fluted layer between two liners. Double-wall board has two fluted layers and three liners, which gives more stacking strength and puncture resistance for heavier products, at a higher cost per box.
Which flute is best for a mailer box?
E flute is the usual choice for mailers because it is thin, folds neatly and takes print well, while still giving useful transit strength. Heavier products may need B flute instead. We confirm the right flute on a physical sample.
Is recycled board strong enough?
For most shipping boxes, yes. Recycled board is our default. For heavy loads, long export journeys or damp conditions, virgin kraft liners can be stronger for the same weight, and we will recommend them where they are needed.
Can you supply FSC-certified board?
Yes. FSC-certified board is available on request for buyers with procurement or reporting requirements to meet.
This page is general information for packaging buyers, not legal advice. Checked on 20 October 2026.
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