Why corrugated cardboard holds its shape
A box wall looks like a pair of flat paper sheets, but between them is a rippled layer called the fluting. The flutes are glued to the outer sheets, or liners, at their raised points. This creates a row of tiny spaces and curved supports across the wall.
When a load presses on the board, the flutes help keep the liners apart. That separation matters: a thicker structure is harder to bend than a single thin sheet of the same paper. The curved flutes also spread pressure across the board rather than letting it concentrate at one spot, while the liners help resist stretching and surface damage.
Strength with little material
The trapped air spaces make the board thicker without filling it with solid material. That gives corrugated cardboard useful stiffness and some cushioning while keeping it relatively light. If a box is squeezed, the flutes can deform and absorb part of the impact; if they are crushed flat, much of that support is lost.
The direction of the flutes matters, too. They run in one direction through a sheet, so the board does not resist bending equally in every direction. In a box, the walls and folds work together, and the vertical flutes can help carry the weight of what is stacked above. A thin layer of shaped paper turns two flexible sheets into a lightweight structural panel.
