Now that we’ve exited what was seemingly the longest winter ever and entered spring, our thoughts turn to all the warm-weather adventures we’re going to have across national and state parks, campsites, climbing walls, and day trails. You might think a snug-fitting top is a garment only for chilly days, but it can be a vital piece of gear for sunny-day treks too. 

The base layer (outdoor industry-speak for “undergarment”) is the foundation for your entire outdoor clothing system, and it all starts next to the skin. From the choice in fabrics to the location of the seams, a lot of engineering goes into an outdoor base layer that sets it apart from a common cotton undershirt. It has to be comfortable and non-chafing, and it needs to wick away sweat to the outer clothing layers so you won’t stay damp. Even on comfortable 70-degree days, you can get hypothermia if you stay wet for too long in a breeze or over the course of a chilly night. There are a lot of undershirts and base layers; few are terrible, but few really stand out. These are our favorites.

Updated April 2022: We’ve added short-sleeve base layer picks for your warm-weather adventures. We’ve added the Patagonia Capilene Cool Daily, Smartwool Short Sleeve, and Smartwool Merino Short Sleeve, and we’ve updated pricing and availability throughout. 

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