Adding fleece liner adds 10 degrees
A removable, machine washable liner is needed for any sleeping bag, simply to keep the bag clean. Use a light nylon "bug bag" in summer or fleece in winter. Adding a fleece liner reduces useable temperature comfort rating by about 10 degs. F. Adding a wind-proof, water-proof, breathable Gore Tex outer protective bag adds about another 5 degs. F. Wearing an insulated head covering, such as a balaclava, dry socks and mittens to reduce heat loss through the top of your head, feet and hands adds another 5 degs. F. If you don't have one already you want a Gore Tex clothes bag to take off the clothes you were wearing during the day. Bring the clothes bag into the sleeping bag with you and they will dry overnight. For winter ops wear silks next to the skin to reduce abrasion and when sleeping wear light weight merino wool or polypropylene long underwear over them. Keep a separate just for sleep wear, while your sweaty ones dry overnight in the clothes bag which doubles as a pillow.
A removable, machine washable liner is needed for any sleeping bag, simply to keep the bag clean. Use a light nylon "bug bag" in summer or fleece in winter. Adding a fleece liner reduces useable temperature comfort rating by about 10 degs. F. Adding a wind-proof, water-proof, breathable Gore Tex outer protective bag adds about another 5 degs. F. Wearing an insulated head covering, such as a balaclava, dry socks and mittens to reduce heat loss through the top of your head, feet and hands adds another 5 degs. F. If you don't have one already you want a Gore Tex clothes bag to take off the clothes you were wearing during the day. Bring the clothes bag into the sleeping bag with you and they will dry overnight. For winter ops wear silks next to the skin to reduce abrasion and when sleeping wear light weight merino wool or polypropylene long underwear over them. Keep a separate just for sleep wear, while your sweaty ones dry overnight in the clothes bag which doubles as a pillow.