The sleeping bag will compress under you reducing it's insulation. If you are weight size concerned you can in theory remove it since loft is what insulated. Ray Jardine of the light hiking community removed the bottom and called it a quilt. I made one and it is fairly effective. The ground pad is great for a tent to make up for this loss of loft, not so good for a hammock. I can not get it to stay in position in a hammock. I have my quilt and a north face mummy rated to 20F. I have been in the hammock with both down below freezing and been comforatable.