Start with the panel and exposure
Specify the flysheet, sidewall or groundsheet separately. A flysheet sheds rain, while a groundsheet can face local pressure from knees, gear and contact with wet ground. Set the required pressure for each panel, then check what the added coating does to weight and packability.
Make the numbers comparable
ISO 811:2018 describes a hydrostatic-pressure test for resistance to water penetration. ISO 4920:2012 measures surface wetting. Specify each separately if your brief requires both, and record the edition, exposed face, specimen condition and acceptance threshold. Request the test report for the actual construction and finish offered.
Compare reference fabrics
The published catalog references include NR13/PTAF6I at 1,000 mm and PP19/ROEO6C at 8,000 mm. These fabrics have different substrates and finishes. Confirm the test conditions before comparing or approving either value.
Check the assembly before release
Test a representative seam, corner and closure where relevant. Fabric-level pressure results do not describe how those parts of the finished shelter perform. Agree which checks will be repeated on the production lot.