Performance underwear is any type of garment worn close to the body and underneath other garments during athletic activities or inclement weather. Such underwear is very often made from synthetic materials that are water-resistant, breathable, lightweight, and close fitting. Performance underwear may include both tops and bottoms, and they may feature short sleeves or short legs, or they may feature long sleeves and full-length legs. The specific features of the underwear can vary significantly according to its intended use and the manufacturer's specifications, but almost all underwear designed for performance is moisture wicking.
Moisture-wicking performance underwear are basically garments that help transport moisture away from the skin to keep the body dry and comfortable during athletic activities. The best performance underwear is both moisture-wicking and breathable, which means air can reach the skin to keep it cool and dry as well. In many cases, the underwear fits close to the body to encourage this wicking property and to improve the comfort of the garments. Bulky underwear can cause hot spots that can lead to rashes or blisters, so tight-fitting underwear with low profile seams are usually preferred.
Most performance underwear is made from synthetic materials, though some underwear is made from a blend of synthetic and natural fibers. The synthetic fibers tend to be lightweight and close-fitting, and they also have a tendency to dry more quickly than natural fibers. Synthetic fibers do, however, have a tendency to absorb odors from sweat, and that odor is often difficult to remove from the clothing, even after several washings. This can be problematic if a person wants to wear the performance underwear in non-athletic settings, though it is not necessarily an issue during athletic activities.
This type of underwear is usually associated with winter or cold weather sports such as skiing, though it can be used in all seasons and conditions. Tight-fitting performance underwear tops may be short-sleeved and exceptionally thin so it can be worn comfortably underneath other garments. This layer will help keep the upper body dry and comfortable in hot weather, or dry and warm in cooler weather. Underwear bottoms may be short-legged and tight-fitting to help prevent hot spots or rashes from skin rubbing against skin or skin rubbing against other garments. Some underwear is sport-specific; baseball sliding shorts, for example, will feature a pocket for a protective cup as well as pads on the thighs to protect the skin when sliding into a base.