Best men's thermal base layers

Top pick: Smartwool Classic Thermal Merino Base Layer Bottom (250 g/m², 100% merino). Merino is the one fabric that stays warm when damp, doesn't get clammy under a shell and resists odor over several days — the bottom to build a cold-weather kit around. It's a slim fit, so size as you would a legging.

Who the others suit:

• Smartwool 3/4 bottom — same merino warmth, shorter leg, so it stops above your boots and doesn't bunch in ski or mountaineering boots.
• KUIU ULTRA Merino 160 — lighter merino blend for active days and milder cold; the Vital PRO Hybrid is the pick for sitting still in serious cold.
• MINTREUS fleece-lined set — best value for a full top-and-bottom set for everyday winter wear.
• Realtree heavyweight pants — for hunting and standing around outdoors; Fruit of the Loom waffle — cheap cotton basics for light cold.
• Reebok long-sleeve top — a synthetic top layer for gym-to-street wear.

Skip the pre-owned Damart pants if you want new.