And these figures can double, even triple, in hot, humid conditions. Cotton's great at soaking up sweat, but it's also great at holding that moisture. A cotton shirt can more than double in weight when it gets wet, and it retains 80 percent more moisture than most high-tech shirts do. A soaked T-shirt will stick to your body, and its coarse, rough fibers may chafe your skin. Some runners avoid these problems by simply not wearing a shirt during the summer.
Many men run bare-chested, and more and more women wear just a sports bra.
But constant exposure to cancer-causing UV light makes this risky. They're available at running stores everywhere. The materials in today's summer running apparel have been scientifically designed to wick moisture away from your skin to the outer surface of the fabric, where that moisture can evaporate quickly. The result is a shirt that stays light, comfortable and cool. We weighed each one dry.