A coil zipper (nylon zipper, spiral zipper) does not have stamped teeth. A nylon monofilament is heat-formed into a continuous helix around a filler cord, then stitched or woven onto the tape. The slider’s internal post squeezes the two helices into mesh or forces them apart. That is why coil is the most flexible, lightest and most colourable chain in apparel — and why it is the wrong answer for a heavy jean wash or a load-bearing pack strap.
TrimGem University teaches coil next to moulded plastic and metal because buyers specify all three on one seasonal BOM. The Guangzhou one-stop catalogue will keep adding chain types; the engineering does not change.
How the spiral is built
Nylon 6 or nylon 66 monofilament is the usual element fibre. The coil is wound on the filler cord, heat-set, then attached to a polyester or nylon tape. Face-up coil shows the spiral on the right side of the garment. Reverse coil puts the spiral to the inside — the visible face is tape, which is how an invisible zipper is constructed (coil on the reverse, special slider). Some mills add a fabric guard on the tape to keep shell cloth from being sucked into the slider mouth.
Coil is also the base for many coated stories: polyurethane film on the tape (water-resistant), extra-thin woven coil without a heavy filler (trouser flies that must not ridge), and two-bone or knitted variants. Those are still coil zippers. They are not a different fastener family.
Gauge, flex and limits
Apparel lives on #3 and #5. #7 appears on tents and heavier sportswear. Closed-end coil is pockets, flies and bag interiors. Open-end coil is jackets and sports shells. Invisible coil is dresses and skirts.
Compared with metal at the same gauge, coil is lighter, quieter, will not rust, and dyes with the tape in a huge shade range. Compared with moulded POM, it flexes around a curve and sits flatter in a seam. The tax: lateral strength is lower; a hot iron or a drying tunnel can deform the spiral; high load at a bag corner wants #8 moulded or metal, not a #5 coil.
Sewing notes that actually prevent returns: do not crash an automatic foot over the coil at the top stop — hand-wheel across or use a zipper foot. Keep the stitch line a few millimetres off the elements so the slider has a path. Trimming loose thread tails is not housekeeping; a tail in the slider mouth spreads the cavity and the chain bursts later.
Reverse coil, lace tape and flies
A reverse-coil closed zipper on a trouser fly gives a near-invisible look without a true invisible slider. Lace-tape invisibles are a dress and blouse SKU: the tape is a narrow lace, the coil still sits on the reverse. Neither construction is for the hip tension of a tight pant side seam, and neither belongs in a heavy denim laundry.
Silver-coated or vacuum-metallised coils exist for a metallic look without metal teeth. Treat the coating as a finish: it can crack, and it is not a brass element.
What to put on the PO
Fibre of the coil (nylon), tape fibre, gauge, face-up or reverse, closed or open, slider lock type, and a wash/iron limit. If the shell is PVC, PE or a coated fabric, demand a tape dye that will not migrate — plasticisers pull colour off poorly bound disperse dyes.
Coil is the volume zipper of the apparel industry for a reason: it sews, it dyes, it bends. Specify it as a spiral on a filler cord with a matched slider — not as “nylon zip, 5#.”