If you don’t have twist ties, cut wire and fold ends with needle nose pliers. These are about 4″ long when finished.
Cut CLOTH RECTANGLES 7.5″ x 14″
Press under each short end 1/8″ and then at the machine, turn another 1/8″ under and stitch for a finished hem.
Fold rectangle to create “envelope.”
Stitch across top flap to create a 1/4″ channel for wire. Insert wire and then stitch channel closed at ends of wire.
Cut FOUR straps — 12″ x 1″
Press in half, then fold sides to center, fold on top of each other, and stitch.
Take the envelope and stitch three pleats per short side for a finished length of 3.5″
Cut TWO facings 4″ x 1.25 or 1.5″
Stitch to wrong side. Lay two straps at the edges, fold facing over to right side and stitch, tucking ends of facing in and capturing straps.
Fold straps back on themselves to the outside and top stitch several times for strength.
Deb found another version below. It offers an elegant simplicity. Three pieces only! No nose wire, but does feature the pocket for filter.
My understanding is that hospitals will wash and sterilize upon receipt but check before dropping off. Many hospitals in the Boston area will accept only masks made from fabric that they supply.