The Classic All-Season Merino Base Layer Long Sleeve is game for anything. With 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 skin. Smooth flatlock seams help minimize chafing and offset shoulder and side seams lie smoothly beneath pack straps and layers. No matter the season or the activity, this base layer is made for it.