Gore-Tex is a waterproof, breathable fabric membrane and registered trademark of W. L. Gore and Associates. Invented in 1969, Gore-Tex can repel liquid water while allowing water vapor to pass through and is designed to be a lightweight, waterproof fabric for all-weather use. It is composed of stretched polytetrafluoroethylene (PTFE), which is more commonly known by the generic trademark Teflon.
Andrew Skurka mentioned why he dislikes Gore-Tex, "Why do I ride GORE-TEX so hard? Let me explain: Because GORE-TEX is not satisfactorily waterproof or breathable. When the name of a product category is an oxymoron, we have reason to be suspicious. Seriously, how can a material prevent the transmission of moisture through it (“waterproof”) while also allowing the transmission of water through it (“breathable”)? According to some questionable technical standards, GORE-TEX may be waterproof and breathable. But it’s completely disingenuous to describe GORE-TEX with the same adjectives that we use to describe glass and rubber, or my cotton pajama pants and running singlets. Moreover, the fabric really only meets these technical standards in a lab. In the field, which is the only test that I care about, GORE-TEX and other WP/B fabrics fail, especially with long-term use and in prolonged wet conditions. While wearing them, I have gotten wet from the outside and the inside, via precipitation and perspiration, and sometimes both simultaneously."