The Smartwool Thermal Merino Base Layer 1/4 Zip has gotten an upgrade to improve functionality while also enhancing aesthetics. As one of their heaviest base layer tops and one of their best base layers for cold weather, this garment uses 100% responsibly sourced Merino wool, shoulder panels, and a flatlock seam construction to help prevent chafing as well as keep you comfortable and temperature regulated as you enjoy high-intensity skiing, hiking, running, and more.