Buyer’s guide
Corrugated Board Explained: Flutes, Walls and Liners
Published 6 November 2026 by Timepack
Corrugated board is a wave-shaped sheet, called the flute, glued between flat sheets called liners. The flute size decides how thick and how cushioned the board is, the number of fluted layers decides whether it is single or double wall, and the liners decide its finish and much of its strength. This guide compares E, B, C and double wall board and shows which suits which job.
Flutes compared
A flute is the wave between the liners. Each size is a different trade-off: small flutes print well and fold neatly, and larger flutes cushion and stack better.
| Flute | Nominal thickness | What it does well | Common uses |
|---|---|---|---|
| E-flute | About 1.6 mm | Thin, with the smoothest print surface | Retail and display packs, mailer boxes, inserts |
| B-flute | About 3.2 mm | Crush-resistant; die-cuts and folds cleanly | General transit boxes, trays, die-cut boxes |
| C-flute | About 4.0 mm | More cushioning and stacking strength | Shipping cartons, archive boxes, protective packaging |
| BC double wall | B and C flute together | Stiffness and stacking strength | Heavy contents, high stacks, pallet layer pads |
Single wall or double wall
Single wall board has one fluted layer between two liners, and double wall has two fluted layers between three. To tell them apart, look at the cut edge of the board: one wavy layer is single wall, two wavy layers is double wall.
Single wall suits most e-commerce, office and storage packing. Double wall is for heavier contents, higher stacks and rougher handling, and it costs more on every box, so it is worth using only where the job needs it.
- Heavy-duty corrugated boxes: when to move up to double wall
Kraft or white liner
Kraft liner is the familiar brown, made for strength, and white liner gives print a clean background. Colours print true on white and darker on kraft, so a brand with a specific colour often chooses white liner, and a plain shipping carton usually stays kraft.
How to read a board grade
A board grade names the outer liner, the flute and the inner liner in order. For example, 150K/B/150T means a 150 gsm kraft outer liner, B-flute, and a 150 gsm test inner liner, where kraft is mostly new fibre and test is mostly recycled. The numbers are the weight of the paper in grams per square metre, so a higher number means a heavier liner.
Containerboard is the industry’s word for the two papers that make up corrugated board: the linerboard and the fluting.
Which board for which job
These are starting points. The right grade depends on the load, so ask for a recommendation and test a sample.
| Job | Start with |
|---|---|
| Retail pack or printed mailer | E-flute, white liner if the print needs it |
| General shipping carton | B or C flute, kraft liner |
| Pizza boxes and food trays | Corrugated board to a food-safe specification, confirmed on the quote |
| Heavy contents or high stacks | BC double wall |
| Pallet layers and slip sheets | B-flute or double wall sheets |
| Wrapping furniture or glass | Single face kraft (SFK) rolls, which flex around the product |
Buying board or boxes from Timepack
Timepack converts corrugated board into boxes in its own factory and sells the same grades as flat sheets.
- Corrugated cardboard sheets: C, B and E flute, whiteliner and double wall, by the sheet
- Corrugated boxes: made to order in any of these boards
- How to measure a box: for your quote
Frequently asked questions
What is corrugated cardboard?
Corrugated cardboard is a board made from a wave-shaped sheet, the flute, glued between flat liners. The arches give it strength and cushioning for its weight, which is why shipping boxes are made from it.
What is E-flute?
E-flute is a thin corrugated board, nominally about 1.6 mm, with a smooth surface that prints well. It is used for retail packs, mailer boxes, display work and inserts.
What is B-flute cardboard?
B-flute is a corrugated board of nominally about 3.2 mm. It is crush-resistant, die-cuts and folds cleanly, and is a general-purpose transit grade.
What is C-flute cardboard?
C-flute is a thicker corrugated board, nominally about 4 mm, with more cushioning and stacking strength than B-flute. It is commonly used for shipping cartons.
What is double wall cardboard?
Double wall cardboard has two fluted layers bonded between three liners. The common grade is BC double wall, a B-flute and a C-flute together, used for heavy contents and high stacks.
Which flute is the strongest?
Double wall board is stronger than any single wall flute. Among single wall flutes, C-flute has more cushioning and stacking strength, while B-flute is more crush-resistant for its thickness.
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