We have added Interfacings to our Face Mask Section as some patterns are suggesting they sit inside the mask as a lining. There are differing opinions on whether this is necessary, or even desirable. Additional layers of fabric will inhibit microbes from passing through the mask but there comes a point where each additional layer provides only minimal improvement. The other consideration is breathability. Some people have been using interfacing interlining which can be sew-in or ironed onto the inside of the mask. We would like to note that although we sell interfacing, we must point out it was not designed for this use.