Bad thread does not always look cheap. It breaks at 5,000 rpm, slubs in the tension discs, crocks onto a light lining, or shrinks a down panel after the press. Incoming inspection is look, untwist, pull, then a few bench tests that a Guangzhou QC table can run before the cone hits a line. TrimGem University files thread faults with zipper complaints: they are why a finished garment comes back, and the checklist stays as the accessory catalogue grows.
What fails in bulk
- Low strength — off-grade fibre or a short-staple spun sold as a sewing ticket. Breaks in the needle, then seam splits in wear.
- Unevenness / slubs / knots — high-speed sewing fuzzes, loops and skips. Regenerated cones show this first.
- Hairiness — extra friction, more breaks, dirty stitch.
- Fastness fail — wash or sun fade; wet crock onto adjacent cloth.
- Shrink or heat shock — a nylon or poorly set polyester that tightens under the iron and arches the panel (a known down-jacket complaint when the wrong fibre was substituted).
Factory symptoms: unexplained needle breaks, seam grin after wash, shade bands on one garment from two cones.
Table checks that earn their time
Cone. Firm tube, clean label, even wind, no crossed layers, no shade jump in the first half-metre. Recycled plastic tubes with burrs shred the first wraps.
Untwist 2 cm. Plies even, filaments or staples not fused. Stuck singles (“并丝”) cut in the needle eye.
Hand stretch. A useful apparel polyester often sits around 15–20% extension and recovers. A dead wire (no recovery) or a gum (too much stretch) both sew badly: cuffs and waistbands split, or the seam puckers.
Abrasion bench. A metre of thread, a light weight, a defined rub: sewing thread should fuzz, not cut. Denim and workwear care about this more than a blouse.
Heat. Ten minutes in ~80 °C water as a crude press screen: commodity polyester should not go board-hard or gummy. Nylon that was never meant to be pressed will tell you here.
Crock. Wet white cloth, defined rubs. Obvious stain is a lining complaint waiting for the first wash.
Burn test — fibre, not quality
A burn test identifies polymer, not whether the lot is on-spec:
| Fibre | Flame | Smell | Ash |
|---|---|---|---|
| Silk | curls, sputters | hair | soft dark bead |
| Cotton | paper-like, fast | paper | soft grey ash |
| Polyester | melts, smoky | faint sweet | hard dark bead |
| Nylon | melts | hair | hard glass-like bead |
Good polyester feels smooth, even-lustred, no grit. Off lots feel harsh, dye in water, or throw acrid black smoke. Burn is a wrong-fibre catch (nylon sold as polyester). Strength and evenness still need a tensile and a yarn evenness method if the PO named them.
Twist, ticket and storage
Z-twist in the lockstitch needle; S-twist where the machine was specified for it. Mixed twist snarls. Ticket must match the cloth (fine 40s/2–50s/2 on light wovens; 20s/2–30s/2 on denim). Fibre must match the job: polyester for most wovens, nylon for stretch and abrasion, cotton for baby hand and hot press.
Three warehouse checks: lot shade (one garment, one dye lot), sealed packing (humid months can raise break rates sharply), storage around 20–25 °C and 50–60% RH.
Name ticket, fibre, twist, fastness method, and lot. A cone that sews today and crocks tomorrow was never inspected — it was hoped.