http://www.rei.com/learn/exper...w-it-works.html REI Elements specifics of waterproof materials specifics of waterproof materials in-depth explanation specifics of waterproof materials Rainwear: How it Works Rainwear: How it Works DWR take the numbers as guidelines and not Gospel. specifics of waterproof materials durable water repellent (DWR) built with materials that breathe well