When designer Carolyn Yim isn’t wearing the merino leggings she designs for Ply–Knits, she swears by Patagonia’s Capilene thermals, which the brand calls its most versatile base-layer bottoms.

Find out more about how we test. I got very excited when I pulled the Assos Thermobooster base layer on at the start of the winter. It's a brand-new addition to the Assos line for this winter and ...