Q: How is a waterproof zipper constructed?
A waterproof zipper combines four elements: a coated or laminated tape that blocks water migration, a chain profile that closes tightly, a slider with a sealed body, and end seals at the top and bottom stops. Many designs also reverse the coil so the teeth sit on the inside, presenting a flat face to the weather.
The tape is the main barrier. Polyurethane coating or a TPU film is applied to one or both faces, and the coating must survive flexing, folding and washing without cracking. The slider is the hardest point to seal, because it must open and close; manufacturers use tight tolerances, internal gaskets or a molded cover, and some add a storm flap or zipper garage for extra protection.
Performance should be quoted as a hydrostatic head for the tape and as a pass/fail result for the assembled zipper under a water-spray or dynamic test. A tape rated at 10,000 mm does not guarantee a 10,000 mm garment, because needle holes, the slider gap and the seam are separate weak points that need their own sealing strategy.