Q: How do I tell if a zipper failure is a manufacturing defect?
Look at where and how it failed. A defect typically appears early, at a consistent location, and shows a manufacturing signature: a missing or malformed tooth, a stop that was not properly set, a slider with an uneven gap from new, or a tape that separates at an unworn seam. Failures that cluster at the same point across several pieces are strong evidence of a process problem.
Wear, by contrast, is distributed and progressive. Teeth polish and thin, plating wears at the contact points, the slider gap opens gradually and the tape edge frays from use. Corrosion from chlorine or salt, heat damage from a dryer and damage from a forced slider are care issues unless the product was specified for those conditions and failed prematurely.
Use a documented inspection: compare against the approved sample, measure length and slider gap, inspect under magnification, and record the wash history and cycle count. Photograph the failure in place before removing the zipper. A fair judgment considers service life, care label compliance and the load the item actually saw, not only the date of purchase.