I have a medium weight down bag (Moonstone) that is good to about 40 F and also have a fitted synthetic liner blanket that goes inside the bag to cover my top side only and extend the range to about 20 - 25 F. Great sustem to cover the temp range you want. I can use liner alone if it is hot, bah alone if it is cool and both together if it is cold. I am very happy with this system... It is also light and compact.