Patagonia Capilene Midweight Crew

I’ve run this as my go-to base layer for close to a year now, through everything from shoulder-season hikes to a week on the Sierra High Route. It regulates temperature well across a wide range, and — unlike a lot of synthetics I’ve tried — it doesn’t start to smell after day three.

The fit is slim without being restrictive, which matters when you’re layering a shell over it on a windy pass. My one real complaint: on mornings below freezing it’s not quite enough on its own, and I end up reaching for a heavier layer sooner than I would with a wool equivalent. For three-season use it’s close to ideal; for winter trips, treat it as a mid-layer rather than a base.