I have seen other threads on this but I thought i would show how I do it.
This time I started with a brand new military 0* mummy bag. Insanely heavy,but cheap and warm. And they are made in the USA if that matters.
sleeping bags 006.jpg
Then I just use scissors to remove the zipper, draft tube, snaps, and hood.
sleeping bags 008.jpg
sleeping bags 013.jpg
Then turn it inside out and sew around the perimeter
sleeping bags 020.jpg
More to come!