Almost every box that ships a product is corrugated, and almost nobody calls it that. The word people reach for is cardboard, which in the trade means nothing in particular. Knowing the difference is the difference between ordering a box that survives a pallet and one that arrives dented.
The structure, and why it is strong
Corrugated board is three pieces of paper doing three different jobs. Two flat sheets, the liners, form the outside faces. Between them sits a wavy sheet, the medium, glued at every peak. That wave is the flute.
The flutes are arches standing on edge. Stood upright, an arch carries far more load than a flat sheet of the same paper, which is why a corrugated box holds weight a stack of equivalent flat board would not. It also explains the single most common handling mistake: lay a box on its side and the flutes are no longer columns, and the stacking strength you paid for is gone.
Corrugated is not the same as cardboard
Cardboard is a casual word covering two different materials. One is paperboard, a single thick ply with no flute, which is what a cereal box or a folding carton is made from. The other is corrugated, with the fluted core. Paperboard folds crisply and prints beautifully but carries almost no weight. Corrugated carries weight but has a ribbed surface that constrains fine printing.
If a supplier quotes you for cardboard without saying which, ask. The two differ in cost, weight, print quality and the load they survive, and the word on its own tells you none of that.
The five flute grades
Flutes are graded by letter, and the letters are historical rather than logical: they were assigned in the order the profiles were invented, not by size. Thickness figures are approximate and vary a little between mills.
| Flute | Approx. thickness | Strongest at | Typical use |
|---|---|---|---|
| A | ~5mm | Cushioning and stacking | Fragile goods, heavy outer cases |
| C | ~4mm | A balance of both | The default shipping box |
| B | ~3mm | Crush resistance, flat surface | Inner packing, sturdier retail boxes |
| E | ~1.5mm | Print surface, low bulk | Mailer boxes, retail-facing packaging |
| F | ~0.8mm | Fine print, minimum bulk | Small premium boxes, cosmetics |
C-flute is the workhorse and the right starting assumption for a shipping box. E-flute is what most custom mailer boxes use, because the thin profile takes print cleanly and still folds into a tidy shape. If you are shipping something heavy or genuinely fragile, A-flute buys cushioning at the cost of bulk, and bulk is billable.
Single, double and triple wall
One fluted layer between two liners is single wall, and it covers the large majority of orders. Double wall adds a second flute and a third liner, usually pairing two different grades so the board resists both crushing and puncture. Triple wall exists for industrial loads and is rarely the answer for a consumer product.
- Single wall: two liners, one medium. The default.
- Double wall: three liners, two mediums, often B and C paired.
- Triple wall: four liners, three mediums. Freight and industrial use.
- Single face: one liner, one medium, unglued on one side. Wrapping material, not a box.
Going double wall when single wall would do is one of the easier ways to overspend. It adds material cost, adds weight, and adds thickness to every dimension, which can push a parcel into a higher dimensional weight band. Specify it when the load or the stack genuinely calls for it.
Choosing without guessing
The honest answer is that flute and wall should be chosen against the actual product, the actual stack height and the actual carrier, not from a table. Tell us the weight, the fragility and whether the boxes will be palletised, and we will specify the board and draw the structure before quoting. The dieline is free and comes back within 24 hours.