How sewing thread is made

Sewing thread is made weaker than the fabric on purpose, so a seam gives way before the garment tears.

stations: 7
things upstream: 19
raw sources: 8
steps from the ground: 7

The short version

Polyester thread starts with chips melted and forced through a spinneret, while bales of short staple fiber are opened, carded and drawn into roving. On a ring spinning frame, filament can run down the middle with staple wrapped around it. Two, three or four such yarns are twisted the opposite way to lock them, then lubricated and wound.

Melt-spin the filament

Polymer chips melt and push under pressure through a spinneret. The filaments cool, gather into a continuous yarn and are stabilized to make the core.

Goes in
Polyester
Open and card staple

Bales of short fiber are opened and blended. Cards separate each fiber from the next and release impurities, then bring them together in a rope called a sliver. Cotton needs an extra cleaning step.

Goes in
Polyester
Draw out the sliver

Typically 6 or 8 slivers run together through rollers whose front pair turns faster than the back. Polyester gets two drawing stages. A speed frame then thins it to roving and adds a slight twist.
Ring spin the singles

Rollers draw the roving finer and a ring frame adds high twist, usually in the S direction. For corespun thread, stabilized filament comes in behind the front rollers so it is not stretched, and staple forms a sheath around it.

Goes in
Polyester
Twist the plies

After clearing and splicing, two, three or four yarns are wound together and twisted in the opposite direction, usually Z. Too little of this finishing twist and the thread frays. Too much and it snarls.
Dye and lubricate

Thread is dyed to color, then treated with lubricant so it runs properly through a sewing machine.

Goes in
Water
Wind and test

The finished thread is wound onto final packages, and samples are checked for strength before shipping.

End of the lineSewing thread Next it goes into airbag, baseball, soccer ball and 48 more.

Worth repeating

Thread weight is often given in tex, the mass in grams of 1,000 meters, and in denier, the mass in grams of 9,000 meters.
In the common weight system for thread, a bigger number means a thinner thread, because it counts the kilometers needed to weigh 1 kilogram.
Garments are usually sewn with thread weaker than the fabric, so a stressed seam breaks before the garment does.