Take fabric of each that measures 9×12.” Adhere interfacing to the wrong side of the fabric.
Fold in half with the fabric on the inside. Sew a 1/4? seam across the top, but make sure to leave a 3? opening in the center.
Slide one elastic strap entirely inside the mask. Pin one end right below the top seam you just made. Pin the other end right above the bottom fold. Sew a 1/4? seam along the side of the mask, making sure to backstitch. Repeat on the other side.
Turn the mask right side out and pin the opening closed. Begin 1? from the top of the mask and are each about 1/2? in size. Pin the pleats in place.
Sew a 1/4? top stitch around the entire mask. This will close the opening, secure the pleats, and finish your mask.