New runners may be surprised to see how warm they get after a few minutes of running, even in the dead of winter. One of the first and probably the most famous of the high-tech athletic clothing fabrics. Gore-tex is waterproof and breathable. It is a membrane attached to outer and liner fabrics that prevents large drops, such as rain, from penetrating but allows tiny droplets, such as perspiration, to pass through and evaporate. Micro Flow Transmission works on the same theory as Gore-tex but at a much more modest price.
Tiny pores allow perspiration to escape but block water and wind from entering.
Widely sold under the LIFA brand name, polypropylene also can be purchased from camping goods suppliers and others at a lower price. There are several generations of polypropylene, so carefully read labels before purchasing. Earlier polypropylene fabric was meant to be line dried. If you wear a wind shell of Gore-tex or MFT, the moisture can pass through the outer layer and evaporate, leaving you more comfortable. It has a soft, silky feel against the skin and its large surface area helps wick moisture away from the body to keep you dry.