How spandex is made

A strand can stretch to five times its length and snap back. It began as a search for a better girdle.

stations: 6
things upstream: 25
raw sources: 11
steps from the ground: 5

The short version

Heat would wreck this fiber, so it cannot be melted and squirted out like nylon. Chemists instead link stiff and floppy segments into a polyurethane chain, dissolve the polymer, and draw the solution through spinnerets while the solvent evaporates. The floppy segments stretch and the stiff ones pull everything back into shape.

Make the stiff isocyanate

Aniline and formaldehyde are joined, then treated with phosgene in closed plants to make MDI, the diisocyanate behind almost all of this fiber. Its ring-shaped units will become the hard sections of the chain.

Goes in
Benzene Formaldehyde Chlorine
Build the floppy diol

Tetrahydrofuran is polymerized with an acid catalyst into long, limp chains with an alcohol group at each end. Ester diols made from adipic acid and glycols are the other option, and they hold up better in chlorinated water.
Join hard and soft segments

The long diols react with the diisocyanate and a short dialcohol such as ethylene glycol. The polymer ends up as alternating rigid and flexible blocks. Diamines then extend the chains.

Goes in
Ethylene glycol
Dissolve instead of melting

The polymer degrades if it melts, so the usual route for synthetic fiber is closed. It is made into a concentrated solution, thick enough to hold together as it leaves a fine hole.
Spin through hot air

The solution is drawn through spinnerets at a temperature where the solvent evaporates. What is left in the air is a solid, rubbery filament.
Wind it for the mills

Filament is wound up and sent to textile mills. There it is usually mixed with cotton or polyester and makes up a small percentage of the cloth, so the fabric keeps the look of the other fibers.

End of the lineSpandex Next it goes into underwear, leggings, swimsuit.

Worth repeating

An estimated 80% of clothing sold in the United States contained spandex in 2010.
A fabric with as little as 5% spandex cannot go through most mechanical recycling machines.
DuPont's Lycra was originally called Fiber K.