Nylon (polyamide) sewing thread is the high-abrasion, high-recovery cousin of polyester. Mills still call it the “king of threads” for a reason: tenacity around 8–10 g/denier, often two to three times the strength of cotton at the same size, and elongation commonly 20–35%. Jeans stress points, bag handles, footwear, tents and automotive seams live on nylon filament. Apparel buyers who only ever bought spun polyester meet nylon when a seam has to move and not cut.
TrimGem University files nylon next to polyester because the Guangzhou desk already samples both tickets on one BOM. The accessory catalogue will keep those constructions in the same conversation as zippers and webbing.
What the fibre actually does
Continuous-filament nylon (PA6 or PA66) is smooth, strong and elastic. PA66 melts higher than PA6 and sits closer to polyester on heat. Indicative behaviour from mill data sheets: yellowing risk from about 150 °C, degradation on long exposure above ~140 °C, stick around 230 °C, melt in the mid-250s °C. Outdoor furniture, sails and tarps that live in sunlight want polyester or a UV-rated nylon, not commodity PA6. FR clothing wants aramid, not nylon — nylon melts.
Abrasion is nylon’s party trick (continuous-filament nylon sits at the top of the usual comparison tables). Mildew resistance is excellent. Long sun still bites untreated nylon. Hydrocarbons (petrol, diesel) are fine; formic acid and hot mineral acids are not; alkali is mostly inert.
Ticket cards for filament nylon use Tkt against dtex and strength. Elongation stays high across the range; dry-heat shrinkage at 150 °C is often held under 3%, boil shrinkage under 1%. Fastness targets of ISO 105 grade 4 on wash and rub are a normal apparel floor.
Bonded nylon and stretch garments
Bonded nylon is filament with a resin coat so plies do not strip in the needle and so high-speed friction does not fuzz the thread. Soft-goods, leather, auto interiors and luggage specify it because a stripped ply is a skipped stitch at speed. Some bonded nylons are sold for elastic seams: a few percent extension with full recovery — useful, but not a substitute for a true covering elastic stitch.
Textured nylon 6 / 66 stretch threads (classic tickets around 70 denier × 2 and 110 denier × 2) are swim and underwear tools. They are not a lockstitch denim thread.
Where it belongs — and where it does not
Use nylon filament or bonded nylon on: workwear stress seams, jeans crotch and belt loops when the mill’s ticket is proven, bags (a large share of better bags), footwear, outdoor pack seams, some seat and technical textiles.
Do not use commodity nylon on: long-sun awnings (polyester or UVR nylon), FR / molten-metal kit (aramid), a hot press programme that will yellow the stitch, or a shade-critical pale garment if the mill has not shown fastness.
Spun nylon exists; volume industrial sewing is still filament, often bonded. Count language (40s, 60s, 80s) still appears on some spun tickets — smaller number, thicker thread, as with cotton count.
Specify PA6 or PA66, filament or bonded, ticket/tex, elongation, UV or not, and press limit. Nylon is not “strong polyester.” It is a different polymer with a different melt, a different stretch and a different sun story.