Strength of Flute Cardboard Types

The flute of a piece of cardboard is categorized by the height and width of each individual flute.
The flute of a piece of cardboard is categorized by the height and width of each individual flute. (Image: Hemera Technologies/ Images)

Cardboard is categorized by flute and wall construction. The flute determines the strength and the wall construction determines durability. Each type of flute and wall construction has a specific use for which it is best suited. Certain types of cardboard are better for shipping heavy items, some types are more impervious to puncture and other types are better for printing and display. In order to keep shipped or stored items free from damage, choose the flute and wall construction appropriate to the situation.


Available flutes for corrugated cardboard are flute types A, B, C, E and F. Strength of flute depends on size; the larger the flute, the stronger the cardboard. The exact size of the flutes can vary depending on the manufacturer, but sizes approximate the following guidelines:

A (coarse) - 3/16 inch high, 33 flutes per foot B (fine) - 1/8 inch high, 47 flutes per foot C (medium) - 5/32 inch high, 41 flutes per foot E (fine) - 1/16 inch high, 95 flutes per foot F (fine/microflute) - 1/32 inch high, 128 flutes per foot

Wall Construction

Each piece of corrugated cardboard is made of two flat sheets separated by the corrugated, or fluted, center. Cardboard in this simple form has been created using single-wall construction. Two layers of corrugated cardboard put together is known as double-wall construction. Manufacturers may put two different types of flutes together to form double-wall corrugated cardboard in order to add durability.


Choose which cardboard to use based on intended function. Boxes for shipping or for moving household goods tend to be a single-wall construction C flute. The B flute is thinner than C flute and, therefore, takes up less space. The smaller flutes make the cardboard more impervious to puncture. A flute is quite strong but not very flexible. E and F flute cardboard are so thin and flexible that printing on them is simple and easy. Double wall construction cardboard takes up a large amount of space but is extremely durable.


Cardboard can be a very strong, durable material under most conditions. However, it is made of paper and is susceptible to moisture. If a box is left out in the rain or submerged in water, most of its relative strength will literally dissolve. Treat cardboard carefully and store in a dry place.

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