Corrugated cardboard boxes are used for packaging, shipping, and storing goods and materials. Corrugated cardboard consists of two pieces of stiff paper with a layer of fluted, or wavy, paper in between. Double and triple wall corrugated don't necessarily have twice or three times the strength of single wall. Single wall consists of a flute layer and two liners. Double wall is made by adding another flute and liner to single wall, so it has less paper than two single walls would. Some multiple wall corrugated materials use different flute types in the second or third wall. Flute type refers to the shape and thickness of the wavy middle layer. From thickest to thinnest, the types are: A, C, B, D, F, E, and N.