The classic cold weather piece from Smartwool, the Merino 250 Baselayer Men's Crew is a fan-favorite, and arguably the piece that started many a convert on the road to wool base and midlayers. Now, to size this piece you need to think about how you’re going to use it. This is a technical, slim, athletic, fit, which means it skims close to the body as you’d expect a layering piece to do. However, this is also the same weight as a feather to light weight wool sweater. Slide a 150 weight baselayer under this and you have a powerhouse combination of warmth, wicking breathability, and easy movement. It’s an especially nice system if you’re climbing or facing a day that starts out cold but warms up by noon. Simply pop off a layer and keep on going. For maximum flexibility and four season wear consider sizing up to give you a more generous fit if you are between sizes. With shoulder panels to eliminate top shoulder seams and a flatlock seam construction helps prevent chafing this is one of the best base layers for cold weather and a piece that when tossed in your gear bag provides cozy comfort all year long. The piece that made converts out of everyone, whether their sport is skiing, hiking, climbing, or biking.