Polyester sewing thread is the volume thread of apparel because it is strong, cheap, colour-rich, low-shrink, mildew-proof and wet-strong. Cotton still earns a hand and a press story. Nylon earns stretch and abrasion. Polyester is what a Guangzhou sewing line is already threaded with at 7 a.m. TrimGem University starts the thread file here; as the accessory catalogue grows, polyester tickets remain the first line on a seam spec.
Three constructions, three jobs
Spun polyester (staple, “cotton-like”) is the most used. Soft, good sewability, high abrasion versus cotton, low shrinkage after heat-set (often <1%). It is the bobbin and the needle on shirts, trousers, knits and most woven garments.
Filament polyester (FDY, continuous) is smooth, bright, high tenacity. Shoe, leather, zipper-tape sew, ski-wear and glove factories standardised on it. Tickets are denier × ply: 150D/3, 210D/3, 420D/3 — higher D is thicker.
Textured / DTY polyester is the stretch knit thread: higher elongation for swim, underwear and active seams that must recover.
Air-textured (ATY) filament tries to steal spun’s cover and filament’s strength: loops on the surface, good for high-speed sewing and outdoor goods.
Corespun polyester puts a filament core inside a staple wrap. Appearance of spun, roughly 50% more strength. It is the lockstitch answer when a factory runs hot and fast and still needs a fine surface stitch.
How spun tickets are named
Staple polyester uses English cotton count / ply. Higher count = finer thread. Typical apparel map:
| Ticket | Tex (indicative) | Use |
|---|---|---|
| 20s/2 | ~29.5 × 2 | denim, shoes, hats, leather |
| 30s/2 | ~19.7 × 2 | denim, bags, buttonholes, bartacks |
| 40s/2 | ~14.8 × 2 | suits, trousers, jackets — the apparel workhorse |
| 50s/2 | ~11.8 × 2 | knits, shirts, dresses |
| 60s/2 | ~9.8 × 2 | fine shirting and light wovens |
More plies at the same count are thicker (20/3 > 20/2). 40s/2 ≈ 60s/3 in greige thickness, not in twist or strength — do not substitute by arithmetic alone.
Needle heat is the polyester tax. A dry needle can spike toward 400 °C; polyester melts well below that. Silicone or wax finishes are a thermal barrier and a friction cut. Cotton survives the same needle better; that is why some corespuns wrap polyester filament in cotton for a high-speed lockstitch that must also take a hot press.
Fastness and chemistry
Disperse-dyed polyester, heat-set, does not lose strength wet. Shade range is enormous. Fastness still needs numbers: wash, rub, sweat, chlorinated water if the garment is swim or hotel white. Metamerism belongs in a light box, not under the office LED.
Polyester is the right default on cotton, synthetics and blends. It is the wrong default only when the spec genuinely needs cotton’s heat, nylon’s stretch and abrasion, or an FR / conductive specialty. Write spun / filament / corespun + ticket or denier + ply + finish. “Polyester 402” is a start (40s/2); it is not a shade or a fastness.