Rashguards are a type of athletic shirt that is typically comprised of spandex and nylon or polyester and are made out of a fast drying material. They are also available in a number of different options, such as long or short sleeve, tight or relaxed fit, etc. While many martial artists simply wear a t-shirt to train, t-shirts can stretch, rip, get wet from sweat and will just end up being super uncomfortable. Rashguards can greatly assist in making your training experience far more comfortable and enjoyable. Rashguards can even help to assist prevent your skin from contacting the mat where bacteria tends to accumulate. Be sure that there are rashguards out there that are made for surfers, scuba divers, and cold weather enthusiasts, these are designed to keep your body heat in, always be sure you purchase the appropriate style that will keep you cool, by purchasing a rashguard from an MMA company or MMA brand.