Q: Are nylon coil zippers strong enough for workwear?
Yes, when the size and construction are specified for the load. A #8 or #10 coil with a heavy tape and a metal slider will handle work jackets, coveralls and utility bags, and it offers flexibility that metal cannot match on curved or bulky seams. The weak point is rarely the chain itself; it is the stitch line, the tape edge or the slider.
Specify a high-tenacity polyester tape, eight to ten stitches per inch, and a slider sized to the chain. Avoid sewing through the teeth: the needle cuts the monofilament and creates a starting point for tooth loss. Bar-tack the ends of the opening so the load is not carried by a single stitch row.
Coil has two genuine limits. Abrasion from sharp edges, concrete or metal filings can shave the filament, and sustained heat above roughly 70 degrees Celsius can deform it. Where those conditions exist, molded resin or metal is more appropriate. For normal industrial laundering and daily wear, a correctly specified coil is durable and much more comfortable against the body.