corrugate means “to form or shape into wrinkles or folds or into alternating ridges and grooves.” So, a corrugated box is one that has rows of small air-filled grooves running the length of the material. They’re made from paperboard and typically have three layers.
The liner board is the flat, thick paper that looks smooth. It makes up the two outside surfaces of the box. Inside those layers is the part with the air grooves called the medium. This is the “corrugated” part of the box. This grooved material, also referred to as the flute, comes in several measurements. Larger grooves provide better cushioning and strength, while smaller grooves provide structural integrity and lower overall thickness.
There are some varieties that only have one outside layer. Some corrugated boxes have multiple layers of medium and liner board for added protection.