Cut the holes for the harness and filters, but haven’t dealt with the trim.
I have two more of the Old Navy cotton masks to play with. Definitely need to deal with the bulky bunching of fabric at the back and I’ll probably remove the inner layer of cotton. It was tricky getting the filters on for a fit check.
This is surprisingly not terrible for a whim.
I tried it on and the cover holds its shape well, thanks to the fabric stiffener. Might add another coat for durability.