When choosing a puffer jacket for extreme cold, the materials used are crucial for retaining warmth. The best jackets typically use either down insulation (from geese or ducks) or synthetic materials. Down is excellent for its warmth-to-weight ratio, with goose down generally being warmer but pricier than duck down. Synthetic insulation has the advantage of retaining warmth even when wet. For the outer layer, look for jackets made with nylon or polyester, which are lightweight, water-resistant, and often designed to be tear-resistant. Some jackets also feature waterproof coatings for extra protection against rain and wind. Additional features that contribute to warmth include a well-designed, snug-fitting hood and adjustable cuffs and hems to seal in heat. By considering these materials and features, you can find a puffer jacket that will keep you comfortably warm in very cold conditions