This is the coolest undershirt you will ever own! It is intended to be worn beneath your cycling jersey, but can just as effectively be worn alone as a tri top or running top, or even beneath a dress shirt for those scorching summer outdoor social events! Constructed of Skin CoolerTM Stretch, this proprietary moisture-radiating material actually offers a cooling effect by dissipating moisture with the slightest breeze caused by movement of the body. If you chose to wear it alone, this fabric blocks 75% of UVB rays.