An ideal lightweight baselayer under your softshell or ski jacket, or worn alone in warmer weather, the Mountain Hardwear Advance Lightweight Long Sleeve Crew for Boys is made of Advance Lightweight fabric, a 100 polyester which wicks moisture, dries quickly and is antimicrobial to keep you feeling dry and nice even during high output aerobic activities. Flat lock seams and strategic seam placement ensure you won't get rubbed the wrong way during a long day in the backcountry.