Sewing thread is not leftover weaving yarn. It is built to run through a needle eye at speed, form a stitch, and then live in a seam: abrasion, needle heat, wash, stretch and recovery. A thread failure wastes shell, labour and a factory hour. TrimGem University treats thread as a garment accessory with the same seriousness as a zipper tape — colour, ticket and fibre on the BOM — and the Guangzhou one-stop catalogue will keep carrying those tickets as sampling grows.
What “sewability” actually means
A sewable thread is even in diameter, smooth on the surface, and strong enough that high-speed sewing does not break it. Practical gates: no unexplained breaks, consistent stitch formation, no skips, evenness, abrasion resistance, and enough surface finish that the needle does not cut the ply. Longitudinal uniformity is why cheap regenerated thread fuzzes in the tension discs.
Aesthetics (topstitch, embroidery-adjacent contrast) add shade match, lustre, fineness and fastness. Performance adds seam strength, elasticity, chemical resistance, flammability and colourfastness to wash, sweat, chlorinated water and pressing.
Fibre, then construction
Natural sewing thread in factories is mostly cotton (and a little silk). Synthetic — polyester and nylon — took the volume because tenacity, abrasion and moisture resistance are higher, and mildew is not a warehouse story.
Construction is the second axis:
- Spun — staple fibres, cotton-like hand. Spun polyester is the world’s default apparel thread: stronger than cotton at the same size, huge shade cards.
- Corespun — filament core (usually polyester) wrapped with cotton or polyester staple. Built for high-speed lockstitch and higher seam strength. A corespun can be ~50% stronger than a comparable spun.
- Filament — continuous. Stronger than spun of the same fibre and size.
- Monofilament — stiff, scratchy; hems and some furnishings, not next-to-skin apparel.
- Smooth multifilament — nylon or polyester; shoes, leather, industrial seams.
- Textured filament — polyester looper thread for coverstitch: bulk and stretch, more snag risk.
Twist (turns per length) too low: fray and break. Too high: snarls and loops. Z-twist is what most lockstitch machines want; S-twist appears on some overlock loopers. Ply is commonly 2, 3 or 4; cabled threads (4, 6, 9 cord) are heavy seams.
Size: ticket, tex, count
Thickness is sold as ticket (Tkt), tex, denier, or cotton count. Rule of use: as fine as the seam strength allows. A coarse thread needs a coarser needle, and a coarse needle cuts light cloth.
Finishes are not decoration: lubricant for needle heat, bonding so filament plies do not strip, non-wick, anti-fungal, FR, water-repellent, anti-stat.
Quality floors
Tensile and tenacity (strength / thickness), loop strength, elongation at break, modulus, shrinkage, moisture regain. Abrasion ranking (illustrative, cotton ≈ 3 on a scale where linen/rayon = 1): spun polyester ≈ 12, continuous-filament polyester ≈ 30, spun nylon ≈ 40, continuous-filament nylon ≈ 150. That is why nylon filament is a shoe thread and cotton is not.
Put fibre + construction + ticket/tex + twist direction + finish + shade/fastness on the PO. “Match the fabric colour” is a dye lot, not a thread spec.