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Inner and Outer Layers
The material used in making corrugated cardboard boxes is called brown kraft paper or paperboard. Kraft paper is made from recycled paper, is typically 40 lb. weight, and is used for many purposes, including grocery bags and school crafts. In corrugated boxes, the layers are called liners, as explained by Technical Association for the Worldwide Pulp, Paper and Converting Industry (TAPPI).
Corrugated Layer
The corrugated layer, or flute layer, fits between the two outer layers, or liners. It is secured with glue. The corrugated layer is also made from brown kraft paper. The corrugation of the paper is performed by a machine called a corrugator. In the machine, the paper is heated, pressed, corrugated and glued. Corrugated boxes can have as many as three flute layers.
Cutting and Printing
The corrugated cardboard gets cut into cardboard box blanks of various sizes as it comes out in a continuous sheet from the corrugator. The boxes then go on to the next stages of printing, cutting and gluing. The flattened boxes are shipped to their destinations. Corrugated boxes are bundled for shipment and are just about the only thing not shipped in boxes.
Variations on the Design
Some boxes are not made with corrugation, but with a single layer or many layers of Kraft paper. Other variations add more layers of corrugation to make even stronger boxes. Boxes that need to carry hefty loads like appliances and furniture can sometimes have up to three layers of corrugation flutes with four layers of the liners. Just one liner glued to a single layer of corrugated paper is called single-face corrugated board and is very flexible, making it perfect for use in packaging fragile items such as light bulbs.