A standard sheet of corrugated board is made from three components: a sheet of corrugated fluted paper, sandwiched between an outside liner and an inside liner.
Each side of the fluting is glued to a sheet of flat liner paper. This gluing fixes the flutes and also gives the lightweight paper especially high stability.
Types of Flutes
Corrugated board made from a single fluting with two liners is referred to as single wall. However, an additional fluting and wall can be glued together to make a stronger board, called double wall. This is suitable for packing heavier goods.
If you need to package extremely large and heavy items (for example, large machine parts), triple wall boxes can be used. This adds yet another fluting and liner.