Many years ago I added a 5' X 6', uncoated ripstop, zip out liner to my 1 person Feathered Friends bag so my wife and I could use it as a 2 person quilt.
Yellow is the bottom uninsulated side and blue is the original sleeping bag. This zip out liner weighs about 7 ounces. So for an additional 7 ounces of weight this one person bag can be converted to a 2 person quilt.
If one wanted something like this on a permanent basis it would be lighter to rip out the existing bag zipper and simply sew the uncoated nylon directly to the bag. The net weight of this modification would be about zero if something like .7 ounce per sy fabric was used because it would weigh about the same as the deleted bag zipper. So one would have (for this bag)a 2 pound two person quilt.
What Worked Well
(1) The yellow bottom fabric made it easy to pull and retain the sides of the sleeping bag close to our bodies.
(2) There were no drafts coming into the bag from the sides
(3) I left the yellow piece unconnected at the bottom so I could stick out my typically too-warm two feet,
What Didn't Work Well
(1) We would get drafts around the head and shoulders.
We found that we didn't like sharing a bag and I couldn't seem to solve the shoulder draft problem so this project hit the shelves. But may be it would just right for you?
