From OpenwaterpediaRash vest, is a type of athletic shirt made of spandex and nylon or polyester. The rash guard protects the wearer against rashes caused by abrasion. These shirts can be worn by themselves, or under a wetsuit. A rash guard by itself is used for light coverage in warm to extreme summer temperatures for several water sports including surfing, scuba diving, snorkelling, freediving, wakeboarding, body surfing, body boarding, windsurfing, kitesurfing, kayaking, or simply for stand up paddle surfing or open water swimming.
There are also lower body rash guards, which are similar to compression shorts to be worn under the surfers' boardshorts, but more specialized for surfers.
Rash guards are most often worn in surfing when the weather is too warm for a wetsuit, and to prevent wax-based chafing from sliding on and off of the surf board, on either the torso, or the legs. A surfboard's wax holds sand from the beach that could rub against a surfer's torso while paddling out to the break, or legs while sitting atop one's board. Rash guards also offer some protection from the sun and slight protection against jellyfish stings. They are sometimes worn under wetsuits to prevent chafing. A rash guard helps to prevent irritation caused by rapid impact with surface water and waves as well.
The use of nylon and spandex create a garment that is lightweight, quick drying, flexible, durable, naturally antibacterial and water wicking.