"Geez, another idea that I had that someone with actual engineering competence already has proceed to try.  I wish them all the luck.Regarding the two questions you had; As far as the measuring process goes, I presume that the custom shirt and suit apps that tailor clothes (apparently) successfully enough to be able to survive, have a technology that can be pretty easily adapted.  As far as the filter issue goes, this appears to me to be the strength of the idea when it comes to commercial success.  The product becomes, like most of the more lucrative businesses, one of periodic purchases forever.  Or they can design a mask that will fit a number of standardized filters.  I myself have actually been surprised at the availability of suitable material to make N95 type filters.  But N95 is a rating, not a material and even using materials that might provide a sufficient level of protection would NOT supply sufficient legal protection.  Even so, N95 rated filters and filter materials can be purchased pretty easily and, while the cost of getting an actual rating as meeting N95 specs may add a large fixed cost initially, the production of one's own proprietary filters would likely be much cheaper going forward.In any case, this product appears to offer a solution for those who have a pre-existing condition that makes being around others a significant risk.  This way, not only does one not have to rely on the "kindness of strangers", they will get better protection than from an ill fitting commercial mask.   "