Smartwool Intraknit Merino 250 Thermal ¼ Zip

Our take Low temps, high effort: That’s the sweet spot for this layer. “Hauling a sled loaded with my toddler and gear through a foot of fresh snow in Montana’s Beaverheads was one of the hardest physical feats I’ve ever done,” one tester says. “I was sweating like crazy in the 10°F weather, but this top kept me from feeling chilled.” The secret: A new, seamless knitting technique used on the 100-percent merino places mesh in swampy zones like the pits, middle of the back, and elbows and a thicker knit across the chest. The bodymapping kept us toasty down to -20°F under a light midlayer and a shell.

The Details We dug the Intraknit Merino’s stretchy, move-with-you fit, which Smartwool augments with
a three-dimensional knit that’s “sculpted” around the elbows (think a sock’s heel)
for more articulation. Bummer: The elbows stretch out after a few days without
a wash.

Trail cred “This layer vented well and dried quickly, even when I was wearing a heavy pack while skinning in Alaska’s Chugach Mountains,” one tester says.

10.5 oz.; m’s S-XXL,w’s XS-XL