Corrugated Cardboard Explained: Flutes & Board Grades
Corrugated cardboard is the workhorse of shipping: light, strong, recyclable and endlessly adaptable. Understanding flutes and board grades helps you pick a box that protects your product without over-spending on material.
What Corrugated Actually Is
Corrugated board is not the same as solid cardboard. It is built from two elements:
- Liners — the flat outer (and inner) sheets that carry print and resist puncture.
- Fluting — the wavy middle layer glued between the liners. Those arches are what give the board its stiffness and cushioning.
Add more liner-and-flute layers and you move from single wall to double wall for heavier or more fragile loads.
Flute Profiles at a Glance
The flute profile is the size and pitch of the waves. Taller flutes cushion better; finer flutes give a smoother surface for printing.
| Flute | Relative thickness | Best for |
|---|---|---|
| A | Thickest | Maximum cushioning, fragile goods |
| C | Medium-thick | General shipping cartons (most common) |
| B | Medium | Sturdy walls, good print, retail |
| E | Thin | Small boxes, crisp printing |
| F | Thinnest | Compact retail and cosmetic packs |
Board Grades and Strength
Grades describe the paper weights and construction. Two figures matter most:
- Bursting strength — resistance to pressure pushing through the wall, useful for bulky or bagged contents.
- Edge crush (ECT) — how much top-to-bottom stacking load the walls take. This drives stacking and palletising performance.
Higher numbers mean a tougher box, but also more material and weight.
How to Pick for Your Product
- Light, non-fragile items: a single-wall B or C flute is usually enough.
- Fragile or heavy goods: move to A flute or double wall.
- Retail-facing packs: E or F flute for sharp print.
- Stacking on pallets: prioritise edge-crush strength.
Boxes come with capacity, material, colour, dimension and pack-size options, so you can match the board to the job. For heavy or pallet orders, a freight option is quoted after you order.
Compare constructions in single vs double wall boxes, then browse our shipping boxes to order from stock.