Gore-Tex® Pro: Using three layers of PTFE laminated together with a suitable backing fabric and a very durable 40 dernier outer with 80 dernier fabric in the high wear areas has resulted in very lightweight, very durable outer shell garments that are both extremely waterproof and very breathable - waterproofs for the professional mountaineer and serious outdoor enthusiast. Gore-Tex as they aren’t necessarily as forthcoming as one might expect with details on breathability and hydrostatic head, probably partly due to discrepancies between testing methods. Anyway, Gore-Tex Pro is “28% more breathable” than previous Gore-Tex ProShell, and has a hydrostatic head in excess of 28,000 mm. That’s the official line. But, in internal testing Mountain Equipment have found Gore-Tex Pro to have a breathability greater than 20,000 g m2 24 hr, a Rate of Evaporation of a Textile of <6 m2 Pa W-1, and hydrostatic head is in excess of 30,000 mm.