The best system for a hammock is to have an underquilt underneath and then an open sleeping bag as a top quilt. You leave the foot end of the sleeping bag zipped up enough to make a foot box that you put your feet in and then you tuck the sides of the bag around your shoulders, hips etc to avoid coldspots and drafts. That way you can move about in the hammock and also regulate temperature much better. No point in zipping it up all the way!The zipper belongs into the middle of the sleeping bag, it doesn't matter if hammock, bivvy bag or Baker tent!
Ultimate versatility was the aim of this systems design so that it suits any trip in any environment. You can use the sleeping bags individually or layer them together to cover all conditions.www.snugpak.com