Gore-Tex is what makes some footwear and outerwear waterproof. The membranes contain over 9 billion microscopic pores that are about 20,000 times smaller than a drop of water – but 700 times bigger than a molecule of moisture vapor. This means water can’t penetrate the Gore-Tex membranes, but moisture vapors can escape it. Gore-Tex garments are made to be waterproof, windproof, and breathable. Some styles of Danner, Chippewa, and Wolverine boots feature the advanced Gore-Tex technology.