Icebreaker uses merino wool in its Men's BodyFit 150-Ultralite Anatomica Short-Sleeve Crew to keep you comfortable in high-aerobic activities like trail running in summer. It regulates your body temperature so you're neither too warm nor too cold. It breathes and manages moisture so you stay comfortable and dry. And it stays fresh after multiple uses. Icebreaker added a bit of Lycra for a body-hugging fit that doesn't restrict your range of motion. And set-in sleeves gives you the freedom of movement you need what you're working out.