I sure didn’t, until Brian from Wings+Horns was nice enough to enlighten me. Ventile cotton was developed during WW2, and is composed of densely woven, long staple fibers. The fibers are woven SO tightly, the cotton becomes, essentially, waterproof. If you didn’t have to stitch a seam into it, it WOULD be waterproof. It also happens to be windproof, and has the ability to endure extreme conditions. Parachuting soldiers and suicide pilots were snuggled up in Ventile cotton long before Wings + Horns decided to adopt it into their Spring 2010 collection. I doubt you’ll be trekking the Himalayas in this outfit. But you COULD, if you wanted to.