You might want to consider an over-quilt rather than a liner. A liner will occupy internal space in the bag and in my experience is just something in which to get tangled if you are any sort of an active sleeper. You could make a down over-quilt from the kit that Thru-Hiker (www.thru-hiker.com) sells. There are plans and instructions available on the web. And, in warm weather, the over-quilt may be enough and could save some weight. I made one with a head-hole in the middle. This way I use it as an insulated poncho also and save the weight of a fleece or insulated jacket. The one I made is baffled and weighs about 17 oz with about an inch of loft.