What Our Gearhead(R) Experts Are Saying:"I wore these on a high summit attempt where the wind chill dropped brutally fast above treeline. The brushed fleece kept my legs warm the entire climb, and I never once felt the cold creep through."Above treeline, where the wind never really stops and the cold sinks in fast, the La Montana Bottom from Hot Chillys earns its reputation as the warmest layer in the pack. Brushed micro denier polyester fleece traps heat without adding bulk, built to sit close to the body under a shell for a high summit push or a long day of backcountry skiing. Moisture-transfer fibers manage sweat as exertion climbs, while a traditional fly and two-tone microfiber waistband add comfort details that hold up through repeated wear at altitude. This is the base layer built for when the forecast turns extreme, and warmth is non-negotiable.