How do I read a fabric test report for waterproof and breathable fabrics?

A fabric test report is only useful if you know which lines decide performance. The five that matter for outdoor shells:

• Hydrostatic head (ISO 811): waterproof rating in mm water column. For jackets: 5,000mm minimum for shower use, 10,000mm hiking, 15,000-20,000mm technical. Always test after washing if DWR durability matters.
• Breathability (ISO 11092 RET): lower is better. RET under 6 = highly breathable for high-output activity; under 13 = good general outdoor; above 20 = noticeable clamminess. Reports in g/m2/24h need conversion - ask for RET for comparability.
• Tear strength (ISO 13937) and tensile (ISO 13934): tear matters more for shell durability, especially lightweight fabrics; specify minimums by fabric weight rather than accepting the mill's standard.
• Colour fastness: to washing, rubbing and light - critical for saturated colourways and high-vis garments (EN ISO 20471 classes impose minimums).
• Shrinkage: after washing - feeds directly into your size grading tolerances.

One habit that saves disputes: require the report to reference the exact fabric batch and construction, and re-test after any fabric change - a membrane switch invalidates every previous number.

See the fabric selection guide this fits into.