Down insulates by trapping air and is prized for being light, easy to compress, long-lasting and breathable. It’s the best insulation in cold, dry conditions, or whenever reducing weight and saving space are top priorities. Warmest weight to warmth ratio. Compressible, if it gets wet it collapses which means more maintenance involved to keep these type of bags and of course once wet then the warmth factor is gone.. Down insulation has typically been sourced from geese. Many major manufacturers have switched to duck down in recent years due to the cost of goose down. The testing and performance standards are the same for both duck down and goose down, so you can be assured you’re getting a high-quality product.