Which zipper keeps a raincoat waterproof?

Q: Which zipper keeps a raincoat waterproof?

A raincoat needs a size 5 PU-coated waterproof reverse coil on a coated tape, with sealed stops, or a welded waterproof zipper in size 5 or 8 on a heavy-duty style. The front is open-end and should be two-way on a long coat. The coating is what makes the difference: a plain coil wicks water along the tape by capillary action, so the chest leaks even when the outer fabric beads water perfectly.

• Size 5 coated reverse coil, or a welded size 5 or 8 zip.
• Sealed top and bottom stops; no bare cut tape ends.
• Storm flap with a sealed seam behind it.

Sewing through the coating is the classic pitfall. Every needle hole opens a channel, and the leak appears at the chest rather than at the seam that was taped. Use a fine needle, seal the stitch line and avoid back-stitching over the coated area. The second failure is an unsealed top stop, which lets water run straight down the inside of the placket.