What Tape Weaving Does
The tape is the structural spine of a zipper. Warp yarns run lengthwise, weft yarns cross them, and the interlacing pattern determines the tape strength, its elongation and, critically, its width. The coil or the metal teeth are sewn or clamped to one edge, so the tape edge is a datum. If the width moves, everything attached to it moves with it.
Weaving is also where the zipper dimensional stability is decided. A tape woven at the wrong density will shrink differently from its neighbour in the same garment, and the difference appears after the first wash as a puckered seam that no amount of pressing will remove.
Equipment and Key Parameters
Narrow-fabric needle looms of 300 to 800 revolutions per minute weave 20 to 100 tapes across a single warp beam. Modern lines include inline heat setting and a width scanner that logs every metre.
- Yarn count: typically 150D to 300D polyester or 200D to 420D nylon in the warp, and 300D to 600D in the weft.
- Warp tension: typically 30 to 80 cN per end, balanced across the beam. Uneven tension shows as a wavy selvedge.
- Weft density: typically 18 to 30 picks per centimetre, giving a tape weight of 25 to 45 grams per metre for standard garment zippers.
- Loom speed: 300 to 800 revolutions per minute; higher speeds widen the shed timing window and increase weft insertion variation.
- Width tolerance: typically plus or minus 0.5 mm on a 25 mm tape, tightened to 0.3 mm for narrow fashion tapes.
- Heat setting: 150 to 180 degrees Celsius under tension for 20 to 40 seconds, which locks the width before dyeing.
- Warp beam quality: yarn tension variation below 10 percent across the beam; beam warping errors propagate through the whole run.
Two loom settings dominate width stability: weft tension and the selvedge holder. Weft tension that is 10 percent high pulls the tape narrow at the fell and lets it recover after take-up, so width alternates along the roll. A selvedge holder set too tight crimps the edge and produces a curl that no heat setting removes. Both are mechanical adjustments made at the start of a run and rarely checked again, which is why width problems cluster at the end of long rolls.
Common Defects
- Width variation along the roll. The most consequential defect. Caused by tension drift, weft density changes or inconsistent heat setting.
- Curling selvedge. Excessive weft tension or an unbalanced weave, producing an edge that will not lie flat at the sewing machine.
- Bowing and skew. Weft yarns run diagonally rather than at 90 degrees, so the tape twists when pulled.
- Density bands. Visible bands where picks per centimetre change, usually from loom stop-start cycles.
- Broken warp ends. Missing yarns create a weak strip that tears at the needle line.
- Contamination. Oil spots, fly and fibre lumps that survive dyeing as dark or light marks.
How the Defect Shows Up Downstream
Beam warping is the upstream cause that weavers inherit. If warp yarns are wound onto the beam at uneven tension, the tape is wide where tension is low and narrow where it is high, and the pattern repeats with every beam revolution. The defect looks like a weaving fault and is actually a preparation fault, which is why width problems often persist after the loom has been re-set twice.
Density bands stay invisible until dyeing. A band with fewer picks per centimetre absorbs less dye and shows as a faint stripe once the chain is coloured, and because the band repeats at the loom stop interval, the stripe appears at regular distances along the finished zipper.
Width variation is the defect that reaches the consumer. A tape that is 0.8 mm wider at one end than the other is sewn into the garment with the same seam allowance, but the finished zipper stands wider in the middle of the panel. After washing, the tape recovers differently along its length and the seam puckers, a fault the garment factory blames on its own sewing and the brand blames on the garment factory.
Curling selvedge shows up as needle deflection. The operator fights the edge, the stitch line wanders 0.5 mm off the tape centre, and the needle starts clipping coil elements. The resulting broken filament is charged to the zipper, although the cause is the loom.
Bowing shows up at cutting. A bowed tape cannot be cut square, so lengths run short at one edge, and the assembler finds one side of the zipper longer than the other when matching left and right halves.
How Buyers Can Judge
- Measure width every metre for the first and last five metres of a roll, and in the middle. Record the range, not the average.
- Cut a one metre length and lay it on a flat table; both edges should be straight within 2 mm. Bow is visible to the eye at this scale.
- Wash a sample at 40 degrees Celsius, tumble dry on low, then re-measure width and length. Shrinkage above 2 percent will cause seam problems in most garments.
- Check pick density with a pick counter at three points and confirm the count matches the specification.
- Inspect the roll edge for broken ends and for tape that has been spliced without marking.
- Ask for inline width scanner logs. A weaver who logs width continuously can prove stability; one who samples cannot. YCC runs inline width monitoring on its tape lines for exactly this reason.
Ask also whether the roll was measured after conditioning. A tape measured straight off the loom is still under loom tension and reads wide; a tape measured after 24 hours on the floor reads the width the garment factory will actually receive.