Boxes are made of corrugated board that consists of two main components: the linerboard and the medium, both of which are constructed from a heavy paper called containerboard. The flat linerboard is adhered to the wavy, fluted medium to form either a single wall or double wall corrugated board.
In single wall board, one layer of the fluted medium is placed between two sheets of linerboard. The outside liner is generally smoother than the inside liner, which is more rippled.
In double wall board, two layers of the fluted medium are alternately placed between three sheets of linerboard. The outside liner is smoother than the inside liner, and the outside corrugated medium is more compact than the inside corrugated medium. Double wall board is used for packaging heavy items that may require increased protection and box rigidity.
The wavy shapes that give the corrugated medium its strength are known as flutes. When adhered to the linerboard, these flutes resist bending and pressure from all directions. The different flute styles provide a range of cushioning, stacking strength and printability to meet any need. Generally, larger flutes provide greater strength and cushioning, while smaller flutes have better printing surfaces and are easier to fold.