Smartwool updated the fit of our Men's Classic Thermal Merino Base Layer 1/4 Zip to improve functionality while also enhancing aesthetics. As one of the heaviest base layer tops and best base layers for cold weather, this garment uses 100% responsibly sourced Merino wool, shoulder panels, and a flatlock seam construction to help minimize chafing as well as help keep you comfortable and temperature-regulated as you enjoy high-intensity skiing, hiking, running, and more.