How denim is made

Denim is blue on one side and white on the other, because only the lengthwise threads are dyed.

stations: 6
things upstream: 4
raw sources: 3
steps from the ground: 2

The short version

Denim is a twill cloth woven with indigo-dyed warp yarns and undyed weft. The warp yarn is dipped in indigo vats and exposed to air to turn blue, rewound onto beams, and woven so the warp mostly covers the face. The finished cloth is sanforized to limit shrinkage and rolled up in bolts.

Dip the yarn in indigo

Warp yarns are gathered into long ropes and pulled through vats of indigo. Natural indigo comes from the indigo plant, though most denim today is dyed with synthetic indigo. Indigo dissolves in water only after a chemical change, and it turns blue again the instant air hits it. Several dips build the color up layer by layer.

Goes in
Cotton yarn Indigo Water
Air it blue

Between dips, the ropes hang in the open air while the dye oxidizes. The dye clings to the outside of each yarn and does not reach the core, which leaves a pale center. This ring-dyed structure is why jeans fade.
Rewind onto beams

After dyeing, the ropes are separated and the yarns are re-beamed in parallel for weaving.
Weave a warp-faced twill

The weft passes under two or more warp threads at a time, which makes a diagonal ribbing. Most denim today is woven on shuttleless looms, and some on old shuttle looms that produce a narrower bolt with a tidy edge called selvedge.

Goes in
Cotton yarn
Preshrink the cloth

The woven cloth is sanforized, a mechanical treatment that shrinks it before it is cut into garments.
Roll into bolts

The finished cloth is inspected and rolled on tubes. Denim usually weighs 11 to 14 ounces per yard, but runs anywhere from 9 to 32.

11 to 14 oz per yard

End of the lineDenim Next it goes into jeans.

Worth repeating

The word denim comes from the French phrase serge de Nîmes, meaning serge from Nîmes.
Over 50 percent of denim is produced in Asia, most of it in China, India, Turkey, Pakistan and Bangladesh.