As a base layer or regular long sleeve, the Mizuno Breath Thermo Top feels incredibly lightweight for the amount of warmth it produces. Mizuno’s signature Breath Thermo fabric uses your own body heat and sweat to generate and retain warmth during your outdoor runs, hikes and winter adventures. As you start to heat up, moisture-wicking fabric with flatlock seams help keep you dry, and a tailored fit with just the right amount of stretch lets you move your arms and torso without restriction. As your outer layer, 360-degree reflectivity helps you to be seen in low visibility conditions. Plus, super convenient thumbholes on each sleeve let you tuck your hands in away from the cold and keep the sleeves from riding up when you’re wearing it as a base layer. The Mizuno Breath Thermo Long Sleeve is a premium base layer and top for winter and cold-weather running. Looking for other cold weather running apparel? Check out our guide on the best winter running apparel.