How leggings are made

Leggings fabric has to rest before anyone cuts it, because knitting and rolling leave it under tension.

stations: 8
things upstream: 35
raw sources: 11
steps from the ground: 8

The short version

Leggings are knit from nylon or polyester yarn blended with spandex, a polyurethane fiber that stretches far and snaps back. The knit tube is dyed, cut in mirror-image leg panels, and sewn with stretch seams. Elastic is stitched into the waistband, and the garment is pressed, checked and folded.

Make the stretch fiber

Spandex is made from a polyurethane formed by reacting a diol with a diisocyanate. The polymer is then dissolved and drawn out through tiny holes into a fine, very elastic filament.

Goes in
Polyurethane
Combine with nylon or polyester

The spandex core is wrapped or twisted together with a harder fiber. The nylon or polyester gives the cloth its look and its strength, and the spandex gives the stretch.

Goes in
Nylon Polyester Spandex
Knit the tube

A circular knitting loom loops the blended yarn into a tube of weft-knit fabric. The tight, smooth knit is what gives leggings their sleek surface.
Dye in a hot bath

The fabric is dyed in a hot bath and then dried. Synthetic fibers take dye under heat.
Inspect and relax the rolls

Rolls are checked for flaws and left to relax. High-stretch cloth stays under tension from knitting, dyeing and rolling, and cutting it straight off the roll gives panels that shrink out of size later.
Cut the leg panels

Cutters cut left and right leg panels and a waist piece from spread layers. The cut pieces have to mirror each other or the finished leg will twist.
Sew with stretch stitches

Flatlock or overlock machines close the inner and outer leg seams and the seat. These stitches are loops, so they stretch with the cloth instead of snapping.

Goes in
Sewing thread
Fit the waistband

A wide band of fabric is folded and stitched around the top, with reinforcement where it takes strain. The finished pairs are inspected, pressed and folded.

End of the lineLeggings

Worth repeating

Spandex, invented by DuPont chemist Joseph Shivers in 1958, can stretch up to five times its length.
Spandex fibers cannot be melted and spun like most synthetic fibers, because the polymer breaks down when it melts.