When it comes to Smartwool® base layers, you deserve a versatile layer that works as hard and often as you do. The year-round Merino 150 Base Layer Short Sleeve can challenge any climate with the body temperature regulating properties and breathability of Merino. This base layer features Core Spun technology—which features Merino wrapped around a nylon core for added durability while still keeping the comfort of ultra-soft, responsibly sourced Merino next to skin. We also added smooth flatlock seams to minimize chafing and eliminated shoulder and side seams so you and your pack can move with ease.