Materials & Board · Quick guide
E flute vs B flute vs C flute: which corrugated flute do you need?
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E flute is the thin, fine flute for printed mailer boxes and lighter products. B flute is the thicker, general-purpose flute for heavier contents and rougher journeys, and C flute is the thickest of the three, chosen for transit boxes that need the most cushioning and stacking strength. If print matters more than protection, start with E; if protection matters more, move up to B or C.
This article compares the three side by side and shows how to choose. For how corrugated board is built, liner types and board grades, see our corrugated board page.
E, B and C flute side by side
The flute is the wavy paper layer between the liners. Its height sets the board's thickness, and the number of flutes per metre sets how smooth and crush-resistant the surface is. The figures below are typical; each corrugator's profiles differ slightly.
| E flute | B flute | C flute | |
|---|---|---|---|
| Typical thickness | About 1.1–1.8 mm (commonly 1.5 mm) | About 2.5–3 mm | About 3.5–4 mm |
| Flutes per metre (approx.) | 290–320 | 150–165 | 125–140 |
| Print surface | Smoothest; fine detail holds | Good; faint ribs possible with direct print | Fair; ribs more likely |
| Resistance to crushing across the face | Highest | Good | Lower |
| Cushioning | Light | Moderate | Highest of the three |
| Stacking strength | Lowest | Moderate | Highest of the three |
| Folding on small boxes | Neat, square corners | Good | Bulky on small sizes |
| Internal space lost to the walls | Least | Moderate | Most |
| Typical use | Printed mailers, retail boxes, displays | Postal and transit boxes, heavier mailers | Transit boxes, bulkier or heavier goods |
What the flute actually does
Corrugated board behaves like a beam. The liners resist bending, and the flutes hold them apart. A taller flute holds the liners further apart, so the board is stiffer when it stands on edge, which is why C flute gives the best stacking strength of the three. Taller flutes also have more room to compress under impact, so they cushion better.
A finer flute has more flutes in every metre. That gives the liner more support points, so the surface is flatter and resists crushing across its face. It is why E flute takes print well, keeps crisp edges and folds neatly, but gives less cushioning when a box is dropped.
In practice that gives a simple rule. Choose the flute for what the box has to survive first, then check the print and fold quality you want is achievable on it.
Choosing by product and journey
Weight, fragility and the journey matter more than any single figure. As a starting point:
| Situation | Usual flute | Why |
|---|---|---|
| Light, robust products: cosmetics, apparel, accessories, stationery | E flute | Neat, well-printed mailer with enough strength for the job |
| Moderate weight or some fragility: candles, glass jars, books, homeware | E flute with a fitted insert, or B flute | Adds cushioning or holds the product still |
| Heavy or fragile items: bottles, ceramics, multiple products | B flute, C flute or double wall, usually with inserts or dividers | Cushioning and stacking strength for rougher handling |
| Boxes stacked in storage or on pallets | C flute or double wall | Taller flutes carry more load on edge |
| Counter display units | E or B flute | Holds its shape on the counter and takes full-colour print |
A fitted insert often does more for protection than a heavier flute. Holding the product still stops it hitting the walls, so a well-designed E flute mailer with a custom insert can outperform a loose product in B flute. Our e-commerce packaging guide covers protection for postal journeys in more depth.
How each flute prints
Corrugated board can be printed in three main ways, and the flute affects each one.
- Direct print onto the liner. Flexographic or digital printing straight onto the board. On B and C flute, the liner is supported only at the flute tips, so solid areas can show faint ribs, known as washboarding. E flute shows it least.
- Litho-laminated. A sheet is printed by litho, then mounted onto the flute. Here "laminated" means glued to the board, not a film finish. This gives the sharpest full-colour result on any flute and is common for premium mailer boxes.
- Digital print on board. Inkjet presses can print full colour directly onto corrugated, which suits short runs and several designs.
If your artwork is detailed or photographic, E flute or a laminated printed sheet is the reliable route. One- or two-colour logos print well directly onto B or C flute, especially on kraft liners. See litho vs digital printing for how the process affects quality and unit cost.
Flute, box size and internal dimensions
The flute you choose changes how much room there is inside the box. Every wall uses up its own thickness, and a roll-end tuck front mailer has double-thickness walls where the sides roll over. Moving from E flute to B flute on the same outside size can take several millimetres off the internal width and length.
That is why we always ask for the product's measurements, not a box size. We work the internal dimensions from the product and then add the board. If you need a particular outside size, for example to fit a postal size band, tell us both, and see internal vs external dimensions and Royal Mail and courier sizes.
When E, B and C are not enough
Three other options come up regularly.
- F flute (micro flute). About 0.8–1 mm, for boxes that need to be slimmer than E flute but stiffer than carton board.
- EB double wall. About 4–5 mm, with double-wall strength and the fine E flute on the printed face.
- BC double wall. About 6–7 mm, the usual heavy-duty grade for heavy, fragile or stacked loads and floor-standing displays.
Double wall adds weight, bulk when stored flat, and cost, so it earns its place only when the contents or the journey need it. For printed transit boxes in single and double wall, see corrugated boxes.
Common mistakes
- Choosing the flute by thickness alone. A thicker board is not automatically stronger; the liners and a fitted insert matter as much.
- Specifying C flute for a small printed mailer. It folds bulkily, prints less cleanly and takes more internal space than the product needs.
- Using E flute for heavy glass without an insert. Fine flutes crush less across the face but cushion less; heavy, fragile items need support.
- Printing detailed artwork directly onto B or C flute. Expect faint ribbing; use E flute or a laminated printed sheet for fine detail.
- Giving a box size instead of product measurements. The flute changes the internal space, so we need the product to size the box.
- Ignoring storage. Corrugated loses much of its strength in damp conditions; store boxes dry and off the floor, whatever the flute.