Q: Why is the waterproof film blistering on a zipper?
Blistering means the film has separated from the tape, or trapped moisture has expanded under heat. Both appear as raised pockets, and pressing a blister gently is a quick way to tell whether it contains air or water.
- Note whether blisters appear after washing, after pressing, or out of the pack.
- Press a blister gently to see whether it contains air or water.
- Check the wash and dry temperature against the film's range.
- Inspect the tape surface under the film for contamination or a dry bond line.
- Cut a small sample blister and look at the bond face.
Blisters after heat exposure point to trapped moisture or exceeding the film's temperature range, which is a care or process issue. Blisters in new stock suggest a lamination defect and should go to the maker with the lot and a photograph of the cut section. Do not puncture blisters on saleable goods, because that creates a leak path.