Lycras and surf shirts primarily protect you from the sun and prevent sunburn with their sun protection factor 50+. They are suitable for surfing, kitesurfing, windsurfing, wakeboarding, wakesurfing, swimming, surfing, high diving, snorkeling, diving, playing water polo, sailing or simply for bathing.
Lycras also prevent rashes (skin irritation) under the wetsuit, but nowadays they are mainly used as sun protection in water sports.
The surf shirts fulfill the same function, but have a looser cut and, in contrast to normal t-shirts, dry much faster. Surf shirts are therefore the ideal companions for travel.