How paper bags are made

A paper bag is a roll of kraft paper folded into a tube and cut so fast that a machine can finish more than two a second.

stations: 6
things upstream: 35
raw sources: 10
steps from the ground: 8

The short version

A paper bag machine unwinds a big roll of kraft paper, folds and glues it into a long flat tube, then cuts the tube to bag length. The bottom is creased, glued and folded to a base, and handles are glued on if the bag needs them. One line can turn out well over a hundred bags a minute.

Unroll the paper

A reel of kraft paper, strong paper pulped from softwood, feeds into the machine. Printed rolls arrive pre-patterned.

Goes in
Paper
Glue on the handles

On carrier bags, a separate unit cuts handle strips or twists paper rope, glues them, and presses them onto the edge of the moving paper.

Goes in
Adhesive
Fold and paste a tube

The ribbon of paper is folded around so its edges overlap and are pasted, giving a continuous flat tube.

Goes in
Adhesive
Cut the tube to length

A knife slices the tube into sections the height of a bag, with the cut timed to the printing.
Crease and glue the base

The end of each section is creased and glue is applied. The base folds into a flat, square-bottomed shape and is pressed shut.

Goes in
Adhesive
Stack and pack

Finished bags are counted into stacks, and a camera or an operator checks for defects.

End of the linePaper bag

Worth repeating

The first machine to mass-produce paper bags was invented in 1852 by Francis Wolle, a Pennsylvania schoolteacher.
Sack kraft paper is made on purpose to be porous, so air escapes quickly while powder is poured in, letting a 25 kg sack fill in about 3.5 seconds.
Charles Stilwell's 1883 bag with pleated sides was called the S.O.S., short for Self-Opening Sack.