20-inch by 20-inch square of cotton fabric
1 coffee filter (optional)
2 rubber bands (or two ribbons)
Lay out the fabric square, right side down, on a flat surface. If there is a selvage edge place it on the left side.
Place the coffee filter on the center of the fabric. Mine had fluted edges, so I ironed it first to flatten it. Note that this step is optional. The coffee filter just adds more filtration, and, unlike fabric, it's a nonwoven product.
Fold the fabric up from the bottom to the halfway point.
Bring the top half of the fabric down so that it covers the coffee filter and the edge meets the bottom edge that you folded up in Step Three.
Fold the bottom up to the center and fold the top over it. After completing this step, you've made a total of four folds since you began.
Slide a rubber band over each end.
Fold the ends to meet in the middle. Tuck the right end into the center of the left end. If your fabric originally had a selvage that you placed on the left side, the selvage edge will be on the outside so that no stray threads or raw edges are showing. Pull the rubber bands to the ends.
Put on the mask by pulling the rubber bands over your ears. Adjust the mask on your face.
If you find that you don't like looping the rubber bands around your ears or it's uncomfortable, you can use ties instead. I used two 28-inch lengths of ribbon for an alternative. Place the ribbons on the fabric, and pull them to the fold at each end. The following picture shows the left end folded.
Center the ribbons so that they are the same length and then tie the top left and right together and tie the bottom left and right together. You can use knots or bows.
With all these layers, it will be difficult to breath if you use a heavy fabric. A quilting-weight cotton should work, or if you don't have any fabric scraps around, you might try fabric cut from an old pillow case or sheet as long as it isn't worn thin.