The microporous structure of the GORE-TEX® membrane makes GORE-TEX® fabrics completely waterproof. Each microscopic pore is about 20,000 times smaller than a drop of water, which means no external moisture — from rain to snow or that puddle you just stepped in — can penetrate the membrane. To keep you comfortable and protected in the windiest conditions, the GORE-TEX® membrane provides an impenetrable wind shield. Your product breathes, but wind stays out. The pores in the GORETEX® membrane are 700 times bigger than a water vapor molecule, so perspiration can easily evaporate and you can stay dry from the inside out.