Spring skiing or summer camping? The year-round Men's Classic All-Season Merino Base Layer Long Sleeve is ready for either. With the Core Spun technology, Smartwool has wrapped lightweight Merino around a nylon core for added durability, while still keeping the comfort of ultra-soft, responsibly sourced Merino next to the skin. They added smooth flatlock seams to help minimize chafing and offset shoulder and side seams to lie smoothly beneath pack straps. No matter the season or the activity, this base layer is made for it.