How cardboard is made

Corrugated cardboard is two flat sheets of paper with a wavy one glued between them, held together with starch.

stations: 6
things upstream: 33
raw sources: 9
steps from the ground: 8

The short version

Cardboard is heavy paper. The corrugated kind used for shipping is a sandwich: a wavy sheet called the medium, made by steaming and pressing paper on geared wheels, is glued between two flat sheets called liners. The sandwich runs through a long machine called a corrugator, which dries it under hot plates before it is cut to size.

Press out the board stock

Thick sheets of kraft paperboard or recycled fiber are made on a paper machine. These are the liners and the wavy middle layer, and they are all stronger than ordinary writing paper.

Goes in
Wood pulp Water
Steam it into waves

At the single-facer, the middle sheet is heated, moistened and pushed between two geared wheels. The teeth squeeze it into a row of folds, called flutes, that run across the roll.
Glue the first liner on

Starch-based glue is applied to the tips of the waves on one side, and a flat liner is pressed against them. This one-sided board is called single face.

Goes in
Adhesive
Glue the second liner on

At the double-backer, a second flat liner meets the other side of the waves. The result is single-wall corrugated board with an arrangement of air channels sealed inside.

Goes in
Adhesive
Dry under hot plates

The new board is carried along a belt over heated plates while weights press down from above. This sets the glue and keeps the board from warping or developing ripples.
Slit to size

Knives trim the edges and slit the wide board into sheets of the width the order calls for. Double-wall and triple-wall board repeat the sandwich for heavier loads.

150 m/min or more

End of the lineCardboard Next it goes into toothbrush, duct tape, fireworks and 16 more.

Worth repeating

Corrugated paper was first patented in England in 1856, to line tall hats, and it was not used for shipping until Albert Jones of New York patented it in 1871 for wrapping bottles and lantern chimneys.
Flute sizes are labeled A, B, C, E and F in the order they were invented, not by how big they are.
Industry and standards bodies avoid the word cardboard because it does not say which product is meant.