Packaging Reference Library · Technical Reference

Corrugated Flute Profiles (A, B, C, E, F and Double Wall)

How flute letters describe the size of the wavy medium in corrugated board, the approximate thickness of each, and which profiles suit shipping, retail and printing.

Ref PK-0103ASTM D4727ASTM D5118

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Corrugated board is made of flat liners glued to a fluted medium. The flute profile—the height and spacing of the waves—is named with a letter. Bigger flutes give more cushioning and stacking strength; smaller flutes give a flatter print surface, better crush resistance and tighter folds. Single wall has one medium; double wall (e.g. BC) has two; triple wall has three. The letters were named in order of introduction, not size.

How to identify

Look at the cut edge: count flutes over a measured length and measure the board caliper.
Box specifications and BMCs often state the flute (e.g. "C-flute 32 ECT").

Flute profiles (approximate)

Flute	Approx. thickness	Approx. flutes per foot	Typical uses
A	3/16 in (about 4.8 mm)	about 33	Cushioning, stacking strength; less common today
C	5/32 in (about 4.0 mm)	about 39	Most common shipping-box flute
B	1/8 in (about 3.2 mm)	about 47	Die-cut boxes, inserts, good crush resistance
E	1/16 in (about 1.6 mm)	about 90	Retail and mailer boxes; good print surface
F	1/32 in (about 0.8 mm)	about 125	Small retail and folding-carton replacement
BC double wall	about 1/4 in (about 6–7 mm)	B + C combined	Heavy or dense products, bulk shipping
EB double wall	varies by maker — check supplier data	E + B combined	Strong, printable display and shipping boxes

Values are typical; corrugators vary, so check the supplier's data for a specification.

Key points

Flute and board grade (ECT or burst) are separate attributes; both belong on the spec.
Flute direction matters: vertical flutes in the box walls carry stacking loads.
Smaller flutes reduce shipping cube and dimensional weight on e-commerce mailers.
Crushed flutes (from tight banding or over-stacking) reduce strength even when the board looks intact.

Common mistakes

Assuming the letters run in size order.
Substituting B for C flute without checking stacking requirements.
Specifying a box by flute alone without a strength grade.

Governing standards: ASTM D4727; ASTM D5118.

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.

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