The major difference between old-fashioned cotton and the other high performance, technical, and/or wicking materials is their dislike of moisture. Depending on the material, each type of high-tech material has it's own method of repelling and/or expelling liquid. Cotton, on the other hand, loves moisture and holds on to it resulting in soaked, heavy, and cold clothing . There are two major factors that make a wicking fabric work: Capillary action and water repulsion.
All wicking materials use a capillary reaction to pull moisture away. Sweat dissipates throughout the material. Areas with a lot of moisture will 'bleed' the liquid to other less moist areas. Once the capillary reaction reaches its threshold the process ceases to work. This is why a wicking shirt will be drenched when you are inside running on a treadmill versus mostly dry after a run outside. The material requires air to circulate so evaporation can take place.
To further aid the 'wicking' process, the fibers are either coated with a water repellent or it is woven into the material itself. A woven repellent is most commonly polyester or a microfiber.(Microfibers are not a fiber unto themselves. It is a technology developed to produce an ultra-fine fiber, and then weave it or knit it into a very high quality fabric. DuPont introduced the first polyester Microfibers in 1989.) A water repellent coating, Gore-tex for example, is a chemical that is added on top of the material itself. Since the treated material hates liquid, water (sweat) tends to bead up instead of absorb into the fibers. This makes the moisture more readily available for evaporation, which in turn, leads to quicker drying.
Is all the hype about wicking really accurate? Some do work better than others and materials use different combinations of the methods listed above to create an ideal level of wicking abilities. Depending on the method, some materials are meant to keep you cool (Coolmax) while others are meant to keep you warm (Polartec). Some are meant to protect you from the elements getting in (Gore-tex) all while allowing air to circulate.