Step 1: What You Need
Step 2: Make Two Darts for Nose and Chin
Make the pie shaped pieces about 1 1/4 inch wide at the edge of the disc. Make the straight sides of the pie pieces 1 5/8 inch long each.
Step 3: Stitch the Darts Together
Step 4: Add the Elastic Strap
Place the mask over your nose and mouth before going out in the cold. It will take a couple of minutes before the mask warms up and begins to keep your breath warm. But, you will be amazed at how well it works. I have used one of these when I jogged down to temperatures as cold as 0 degrees F. and it kept my breath quite warm. The mask will absorb a lot of moisture from your breath. When I jogged with it at 0 degrees F. an icicle more than an inch long formed at the bottom of the mask.
Wash the mask in warm water periodically and let it dry.
Udate: I do not have my original mask, nor do I have the materials to make one. For demonstration purposes I cut a disc from a sheet of paper and used cellophane tape to close the darts. You can see how that forms the mask to cover your nose, mouth, and chin. Attach the elastic strap so the strap goes above your ears and around your head. The mask will fit against the face as in the right side of the photo, not as on the left side where my fingers cause it to bend away from the face for the purposes of holding it.