Spring skiing or summer camping? The Classic All-Season Merino Base Layer Long Sleeve is game for either. 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. 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.