A moulded plastic zipper (resin zipper, acetal zipper, often called Vislon after the YKK trademark, or “塑钢” in Chinese mills) has discrete POM (polyoxymethylene, acetal) elements injected onto the tape bead. The teeth are blocks, not a nylon spiral. That is why the chain looks chunky, holds a colour in the tooth itself, and stays usable in the cold when a metal slider would freeze to a wet chain.
Coil is the flex and weight answer. Metal is the jeans-wash answer. Moulded POM is the outerwear and bag answer — the chain TrimGem University puts next to snaps and cord locks on a winter BOM, and the same chain the Guangzhou platform will keep sampling as the catalogue grows.
How the teeth are made
Molten POM is injected through a precision tool onto a polyester tape. Teeth and tape are one shot, not a later clamp. Tooling tolerance in a serious house is on the order of ±0.02 mm on tooth pitch — the same order of magnitude that keeps a slider from chewing. Colour is in the resin or a masterbatch, so the tooth colour is not a plate that can wear to grey metal.
POM’s useful window is wide: mills quote roughly −40 °C to 100 °C for the polymer, with house specs often guaranteeing function from about −30 °C to 80 °C. It will not rust. It is lighter than a metal chain of the same gauge. The tax is heat: a press, a drying tunnel or a car dashboard in summer will soften teeth, close the box mouth, shrink the pin, and let the slider walk off. Do not iron moulded chain. Do not copy a cotton-garment press programme onto a POM fly.
Open/close life on a commodity moulded zipper is often specified at 10,000 cycles; higher programmes claim 50,000. Those numbers are mill claims until they sit on a test report against QB/T 2172 or the brand method.
Gauge and where it belongs
#3 moulded is a light jacket and kids’ outerwear chain; the tooth is still blockier than #3 coil, so the seam is more visible. #5 is the down-jacket, ski-shell and sports-bag default. #8 and #10 are travel bags, heavy outerwear and industrial covers.
At the same gauge, moulded chain usually offers higher lateral and fold strength than coil, and a coarser, more “technical” face. Smoothness of the slider is typically a little worse than coil — the tooth is a brick, not a spiral. That is a hand-feel choice, not a defect, unless the slider cavity is wrong.
Open-end process sheets change with gauge: #5 moulded open-end end-tape and element count are not the #8 numbers. Pressure and dwell on the pin-and-box set should be raised for the heavier chain. Copying a #5 setup is how boxes pull off in packing.
Visual SKUs that are still POM
Gold- or silver-look teeth, translucent and semi-translucent teeth, glow, laser, and rhinestone-inlay teeth are all moulded plastic with a decorative face. The inlay sits on a large tooth table — one reason designers like POM for jewellery zippers. The mechanical spec does not change: pitch, slider mouth, stop strength.
Wax on the teeth is an acceptable mill lubricant. Sticky oil is not: it holds dust and turns into grit in the slider.
Spec line
Name POM / moulded / Vislon-type, gauge, closed or open, slider lock, tape fibre, and an iron/press limit. If the garment will be garment-washed, say so — some decorative coatings on plastic teeth do not survive enzyme or high pH.
Moulded plastic is not “the cheap metal zipper.” It is a different chain, tooled for cold, colour and bulk. Put it on the jacket that needs that, and keep coil on the dress.