Architects have known for thousands of years that an arch with the proper curve is the strongest way to span a given space. The inventors of corrugated fiberboard applied this same principle to paper when they put arches in the corrugated medium. These arches are known as flutes and, when anchored to the linerboard with an adhesive, they resist bending and pressure from all directions.
When a piece of combined board is placed on its end, the arches form rigid columns, capable of supporting a great deal of weight. The flutes act to keep the linerboard sheets separated, maximizing the bending rigidity of the board. When pressure is applied to the side of the board, the space in between the flutes acts as a cushion to protect the container’s contents. The flutes also serve as an insulator, providing some product protection from sudden temperature changes. At the same time, the vertical linerboard provides additional strength and protects the flutes from damage.
Flutes come in several basic designations. Flutes with the same designation have similar size, but may have various flute profiles and number of flutes per foot within a given designation:
A flute was the original flute profile for corrugated board. It has about 33 flutes per foot.
B flute was then developed for canned goods that were self-supporting, and so did not require boxes that supported much load. It has about 47 flutes per foot.
C flute was next developed as an all-purpose flute, and it has about 38 flutes per foot.
E flute was the next successful flute profile, and it has about 90 flutes per foot.
F flute was developed for small folding carton type boxes. It has about 125 flutes per foot.
In recent years not only has there been a proliferation of flute profiles, but there has been increase in the variation in flute characteristic measurements for any given flute profile. Flute profiles will vary, sometimes significantly, because the corrugator rolls are manufactured to address a variety of aspects (such as speed, paperboard characteristics, economies, etc.).