Both types of zippers feature their own strengths and weaknesses.  Nylon Coil zippers possess stronger horizontal pull-strength against separation which is why they are often found on travel luggage or other items prone to overstuffing.  However, because the Nylon Coil teeth are sewn onto the zipper tape, it’s possible for the teeth to separate at this potential weak point.

While the Nylon Coil zipper is “stronger” than the Molded zipper under ideal conditions, its teeth’s coil design is more prone to trapping dust, debris and contamination and therefore will prematurely wear out without proper cleaning and lubrication.  Conversely, Molded zippers feature separate individual teeth that are directly molded to the tape and intrinsically excel at shedding impurities.  Furthermore, the Acetal material is inherently self-lubricating and provides for long-term low-maintenance use.  Because of these characteristics, Molded zippers tend to have a longer service life when compared against Nylon Coil zippers.

That said, Nylon Coil zippers are “self-healing,” meaning when the zipper accidently opens or closes incorrectly and skips a tooth, these misalignments are easily correctable by merely zipping the slider over the problematic area.  On the contrary, misalignments on a Molded zipper usually indicates or results in a damaged tooth, which oftentimes renders the entire zipper inoperable and requires a full zipper replacement.