The Patagonia Capilene Lightweight Zip-Neck uses a recycled polyester double knit and plant-based HeiQ Mint odor control, along with a zip that vents heat the moment the pace climbs. An underarm gusset keeps the reach open on steep terrain without binding at the shoulder. What Our Gearhead(R) Experts Are Saying:"I wore this under a jacket on a cold approach that turned into a full-value bushwhack, and dropping the zip kept me from soaking through before the real climbing even started."