A very poor conductor of heat silk will trap a lot of warmth within your sleeping bag making it a very warm compact unit. A silk liker is also a must when traveling in hotter climates its natural heat managing characteristics keep the body comfortable in both extremes of hot and cold. Ounce for ounce our most heat efficient liner. A sleeping bag liner helps keep your sleeping bag free of dirt and body oils and a clean bag does not require laundering as often and will last much longer. A bag liner also provides anywhere from 5F to 15F of extra warmth to your sleeping bag.