Corrugated fiberboard, or combined board, has two main components: the linerboard and the medium. Both are made of a special kind of heavy paper called containerboard. Linerboard is the flat facing that adheres to the medium. The medium is the wavy, fluted paper in between the liners..
The following illustrations demonstrate four types of combined board.
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 paperwhen they put arches in the corrugated medium. These arches are known as flutes and when anchored to the linerboard with a starch-based 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. 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 more strength and protects the flutes from damage.
Flutes come in several standard shapes or flute profiles (A, B, C, E, F, etc.). A-flute was the first to be developed and is the largest common flute profile. B-flute was next and is much smaller. C-flute followed and is between A and B in size. E-flute is smaller than B and F-flute is smaller yet.
In addition to these five most common profiles, new flute profiles, both larger and smaller than those listed here, are being created for more specialized boards. Generally, larger flute profiles deliver greater vertical compression strength and cushioning. Smaller flute profiles provide enhanced structural and graphics capabilities for primary (retail) packaging.
Different flute profiles can be combined in one piece of combined board. For instance, in a triple wall board, one layer of medium might be A-flute while the other two layers may be C-flute. Mixing flute profiles in this way allows designers to manipulate the compression strength, cushioning strength and total thickness of the combined board.
Standard US Corrugated Flutes
|Flute Designation||Flutes per lineal foot||Flute thickness (in)||Flutes per lineal metre||Flute thickness (mm)|
|A flute||33 +/- 3||3/16||108 +/- 10||4.8|
|B flute||47 +/- 3||1/8||154 +/- 10||3.2|
|C flute||39 +/- 3||5/32||128 +/- 10||4.0|
|E flute||90 +/- 4||1/16||295 +/- 13||1.6|
|F flute||128 +/- 4||1/32||420 +/- 13||0.8|
Dimensions are given in the sequence of length, width and depth. Internationally, the words length, breadth and height may be used to express these dimensions. The dimensions of a box are described based on the opening of an assembled box, which can be located on the top or the side, depending on how it is to be filled. The opening of a box is a rectangle; that is, it has two sets of parallel sides. The longer of the two sides is considered its length, the shorter of the two sides is considered its width. The side perpendicular to length and width is considered the depth of the box.
Dimensions can be specified for either the inside or the outside of the box. Accurate inside dimensions must be determined to ensure the proper fit for the product being shipped or stored. At the same time, palletizing and distributing the boxes depends on the outside dimensions. The box manufacturer should be informed as to which dimension is most important to the customer.
|Linerboard Performance Standards|
|Max Wt. Box/Contents
|Min. Burst Test Single/Double Wall
(lbs. per sq. in.)*
|Min. Edge Crush Test (ECT)
(lbs. per in. width)
|Single Wall Corrugated Boxes|
|Double Wall Corrugated Boxes|
|Triple Wall Corrugated Boxes|