I was thinking about an idea for an underquilt. It would essentially be an empty bag made from ripstop silnylon with baffles running lengthwise and open at one end and with draw cords at each end so that the ends could be cinched up. These baffles would be stuffed with leaves, ball moss, etc. Has anyone tried such a thing? Would the insulative value amount to anything? It would certainly be cheaper than a down-filled underquilt. Something similar could be used for a top quilt as well. Would it be better to make them out of a breathable material?