Place the mask pieces right sides together. Add the filter pieces to either side of one pair.
Insert it between the layers in the center along one edge.
Stretch it until it curls. You will need two pieces. The length depends on if you want ties or loops to go around your ears. I prefer the loops with bead adjusters.
The ties can be adjusted with the beads around the ears. I tie an overhand knot on each end so the tie won’t accidentally pull out of the bead.
If you cut long enough ties, the mask can be tied on if that is preferable.