Spring skiing or summer camping The year-round Merino 150 Base Layer Long Sleeve is game for either. With their Core Spun technology, they've wrapped lightweight Merino around a nylon core for added durability, while still keeping the comfort of ultra-soft, responsibly-sourced Merino next to skin. WThey added smooth flatlock seams to help minimize chafing and offset shoulder and side seams to lie smoothly beneath pack straps. Select colorways feature a more responsible plant-based-dye technique. No matter the season or the activity, this base layer is made for it.