I assume you are reffering to the DRI FIT technology

Which is a  microfiber that works to keep you comfortable - transporting perspiration from your skin to the outside for rapid evaporation. Work out. Sweat. Stay comfortable. Dri-F.I.T. fabric wicks moisture away from your skin to keep you dry, especially where light weight is important. As moisture is produced by the body, it moves quickly through the first (hydrophobic or water-hating) layer of the Dri-F.I.T. garment. This layer neither absorbs nor slows down the moisture; instead, it acts as a pump or syphon, delivering the moisture to a second (hydrophylic or water-loving) layer, which disperses the moisture across the outer surface for rapid evaporation. Dri-F.I.T. fabric - lightweight, breathable comfort.

Here is a web page with NIke's terminology about the different kinds of fabrics and their functions:

http://reviews.ebay.com/Nike-Apparel-Clothes-Clothing-T-Shirt-Hat-Cap-Socks_W0QQugidZ10000000004646221