I'm going to jot down a few notes on how I am frantically creating my own original design for homemade barrier masks for the COVID-19 health threat. An avid sewer should be able to get the gist of my design from this, but I hope to come back as time permits to fill in details...
7x9" lining can be cut 6x9 for a good all around fits all size. 3/8 seam allowance and a 1" casing at top. (UPDATE: mens are better at 8x9.5"!!!!)
Lined. One side is longer to create a casing. Right sides together inserting elastic. Trim corners to decrease bulk.
Pleat them up like an accordion (I do 2 pleats) and iron and pin, top stitch through all layers. Try to arrange your pleats so that you have the same amount of layers to sew through the entire length of each side instead of having mountains and valleys.
(Kids and adults shown here)
One improvement I have been making (thanks to my EMT friend Jamie Brown!) for healthcare workers is where the lining creates a pocket so that a 3rd barrier could be inserted.
These apparently can be purchased to greatly improve the barrier. (Photo credit Jamie Brown!)
Bonus for using novelty fabrics! Keeping it kid-friendly and making a statement other than one related to illness.