Flute Profile Chart

What it is

Corrugated board has flat liners glued to a wavy medium. The wave shape is the flute. Flutes are named with letters. The letters were assigned in the order the flutes were introduced, not by size, so the letters do not run from big to small. Larger flutes give more cushioning and stacking strength. Smaller flutes give a smoother print surface, tighter folds and less shipping cube.

How to identify

1. Look at a cut edge of the board.
2. Measure the board thickness (caliper) with a ruler or caliper.
3. Count the flutes over a measured length, such as 6 in, and scale to a foot.
4. Match both numbers to the chart.
5. Count the layers of medium: one is single wall, two is double wall, three is triple wall.

Flute profiles (approximate)

Values are typical. Corrugators vary, so use the supplier's data for a specification.

Key points

• Flute and board grade (ECT or burst) are separate. Put both on the spec.
• For stacking strength, the flutes in the box walls should run vertically.
• Switching flute changes the outside dimensions of a box with the same inside dimensions. Check pallet patterns and dimensional weight.
• Smaller flutes resist crushing better under printing and handling but give less cushioning.
• Crushed flutes from tight straps or over-stacking reduce strength even if the box looks fine.

Common mistakes

• Assuming the letters run in size order.
• Substituting B for C flute without checking stacking needs.
• Ordering by flute only and leaving out the ECT or burst grade.
• Measuring board thickness on a crushed edge.

Governing standards: ASTM D4727 (corrugated and solid fiberboard sheet stock); supplier specifications for flute dimensions.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.