Warmest Capilene weight; may be worn as a base layer or over Lightweight or Midweight. depending on conditions. Worn alone. it is perfect for climbing or hiking at altitude. Excellent second layer for stop-and-go activities. Cut trim for layering; order a size up to use as an outer piece. FABRIC: 6-oz. double-faced Capilene-treated polyester fleece. M's Expedition Weight Fleece Capilene Bottoms