The SmartWool Men's PhD Ultra Light Long-Sleeve Shirt brings lightweight warmth without stifling you on daily runs and heart-pumping workouts. Breathable mesh panels channel cool air across your upper body to prevent you from overheating. The merino wool blend actively pulls perspiration off your skin to promote evaporative cooling. Another key benefit to merino wool lies in its ability to prevent the growth of odor-causing microbes. Ultimately, this means it'll stay fresher than pure polyester training tops, even during distance runs and intense workouts.