Gore-Tex is a textile manufactured out of synthetic materials that is designed to be waterproof and windproof while at the same time allow moisture to permeate outwards thus offering the wearer a comfortable experience.
The waterproof nature of Gore-Tex is a result of layers of semi permeable membranes that are used in its construction. Each of these membranes have microscopic holes that, while small enough to allow water vapor to pass, are too small to allow liquid moisture in. The unique semi permeable membranes that make Gore-Tex possible were invented by Robert W. Gore, Wilbert Gore and Rowena Taylor. Interestingly these membranes are constructed out of the same material that is used to put Teflon coatings on pots and pans.
Gore-Tex is most commonly used in activewear including coats, shoes, gloves, pants and hats where its water resistance and breathability are welcome features. The main drawback of Gore-Tex fabric is the limited durability of the Teflon coating that provides water resistance. Because the pores are susceptible to clogging from dirt and body sweat Gore-Tex must be kept immaculately clean to maintain a high level of performance; however early forms of Gore-Tex lacked the protective barriers necessary to keep the Teflon coating intact. This was later remedied by adding a protective layer on both sides of the Teflon however this protective layer reduced the ability of the Teflon to allow moisture to pass out of the clothing thus limiting the effectiveness of Gore-Tex. While Gore-Tex once held the lion’s share of the activewear market it has recently come under attack from other types of water resistant fabrics that perform just as well yet do not have the same limitations as Gore-Tex.
For more info on high-tech fabrics and "smart" synthetic fibers, please check out this blog post.