OutdoorGearLab

Smartwool comes out with another winner, especially in colder temps, with the  Smartwool Classic Thermal Merino 1/4 Zip. We found this layer warm, breathable, and versatile &mdash; not to mention extremely handsome to wear. "Classic" may be in the name, but this base layer comes with a few new features built upon the rock-solid legacy of its brethren. A front quarter zip helps dump any excess heat you may have built up trouncing around a winter wonderland. The top shoulder panel helpfully moves the top seam that would be on the crest of your shoulders down and out of the way from heavy pack straps that can cause discomfort. Wool is an almost perfect natural fiber to use for base layers, and the 100% Merino wool utilized in the Classic Thermal Merino is some of the highest quality we've reviewed. 
Since this top excels in colder conditions, it will feel a little overkill when worn in the heat. When it's beginning to look a lot like summer outside, store this base layer in the closet until the first new flakes start to fall again, and pick out a more appropriate base layer to be comfortable in instead. Despite all the amazing characteristics of Merino wool, one of its weaknesses is durability: wearing it around town for an aprés ski drink will be fine, but pit it against anything abrasive, and you'll earn yourself a night watching movies while sewing on patches. Be mindful when washing and drying too, as improper care can cause undue wear to the Classic Thermal, shortening its lifespan. 
Read more: Smartwool Classic Thermal Merino 1/4 Zip review

Merino Shirt Comparison