I had a quart of down left over from the down jacket reconstruction I did a couple of months ago. Just recently, the idea came to me to use this down to make a muff.
To contain the down, I made a tube of closely-woven fabric, a little more than twice as long as the muff, and wide enough to enclose both down and hands easily. Then I pulled one end of the tube up inside the other, making a double-walled tube. I stuffed the down into it between the walls--that stuff goes everywhere--then folded down and pinned the raw edges, and sewed it closed.
I did some gentle pushing and pulling at this point to distribute the down more evenly.
For a lining, I chose some scrap cashmere (handed down) in black, and sewed that into a tube. For the outside, I used some shirred plum velvet (also handed down), again made into a tube. I sewed the ends of these two tubes together (the last seam by hand).
Then, for a cord, I covered a piece of rug yarn with more of the plum velvet, with raw edges out because I didn't feel like turning a long tube right side out. I ran the cord through the muff before I joined the ends.
The muff is cozy and very warm.