New to Smartwools innovative Intraknit line is the Mens Intraknit Thermal Merino Base Layer 1/4 Zip. This Smartwool base layer is 3D-mapped for a near-custom fit and freedom of movement. Its engineered construction helps enhance your performance with a lighter weight and cleaner finish. If youre looking for base layer clothing for cold weather, this one uses Merino Sport yarn that combines the power and benefits of Merino wool with the durability and fast dry times of polyestercreating the ultimate performance-ready top for all of your high-energy activities.