Warmth Despite its gossamer-feeling fabric, this top packs serious heat: “It’s a lightweight layer that’s as warm as a medium-weight,” says a tester who took it comfortably down to -10°F in the Colorado Rockies under a fleece midlayer and shell. Why? ExOfficio’s S° Warm fabric incorporates two tricks: One, hollow-core synthetic fibers trap warm air. Two, tiny bits of ceramic dust embedded in the fabric absorb body heat, returning warmth to the skin.
Wicking Testers overwhelmed the wicking power easily during sweatfests, but the ultrathin material dried in a snap.
Stink resistance The lack of funk was impressive for a synthetic, thanks to a silver ion antimicrobial treatment called Silvadur: One tester wore it four days straight on a hut trip, reporting minimal BO. And the treatment didn’t wear off after months of use.
Features A generous zippered pocket near the hem fits a smartphone and keys. But if you’re running, everything in the pocket bangs against your leg with each step. The men’s version has buttons instead of a ¼ zip like the women’s (pictured). It also comes in hoody ($85) and crew ($70) styles for men and a V-neck for women ($65). (m’s L); m’s S-XXL, w’s XS-XL