Smartwool took their popular Classic All-Season Merino Base Layer and added a 1/4 zip to it-making it the perfect base layer for warm or cold weather. This top uses their lightest-weight Merino fabric wrapped around a nylon core to increase durability, while still keeping the 100% soft, Merino wool you love next to skin. Side seams help minimize chafing while wearing a pack and offer a body-enhancing fit. This base layer is comfortable, powerful, sustainable, and, frankly, do-it-all-able. Fit & Design: Slim fit Light weight Merino jersey fabric uses a nylon core to increase durability while still keeping 100% Merino wool next to skin Offset shoulder and side seams designed to increase comfort and minimize chafing while wearing a backpack Side seams wrap to front for body-enhancing fit Flatlock seam construction designed to minimize chafing 8" (20 cm) center front zip with semi-locking slider