Our insulated Field Flannel Shirt combines a classic cotton flannel with high-performance insulation for a shirt that excels in cold weather. The midweight flannel fabric, heavily brushed on both sides for softness and warmth, is tightly woven for durability. The 60g PrimaLoft® Gold insulation features the highest warmth-to-weight ratio in synthetics and is quite packable. Originally developed as an alternative to goose down, this polyester insulation breathes well and retains 98% of its insulating abilities even when wet. Virtually unbreakable melamine buttons are used for the front closure and adjustable cuffs. Center-back box pleat for ease of motion.