Q: What is a molded resin zipper made of?
Molded resin zippers are made from acetal resin, usually a polyoxymethylene (POM) compound, injected directly onto a polyester tape. The molten resin fills a rotating mold that forms the teeth and the connecting element in one continuous strip, so each tooth is mechanically keyed to the tape rather than sewn on.
POM brings useful properties to a zipper: low moisture absorption, good dimensional stability, resistance to most detergents and a wide service temperature, generally from about minus 20 to 60 degrees Celsius. Color is added as masterbatch, so the tooth color is solid through the section rather than a surface coating, which is why molded resin resists chipping and keeps its shade after abrasion.
The limits matter too. Resin softens if pressed at high iron temperatures, and it can become brittle in very cold conditions or after prolonged UV exposure unless the compound is stabilized. Tooth size is coarser than coil at the same strength, so molded chains are visually heavier. Ask for the base polymer and any UV or flame-retardant additives if the product is outdoor or safety related.