The zip line affects closure, but a visible gap alone does not prove heat loss or its cause.
Inspect it empty first
Close the zip slowly. Look along the teeth, ends and corners.
Repeat under load. Place representative packs used on site. Note whether the liner catches or closure changes with the load.
Record what you find
Photograph snag location, any open section and seam condition. Use the same method at the next check.
A visual check records a finding; it does not measure performance alone.
