JPL
Using flexible filament this design is focused on conforming to a wide range of faces and fast printing. This means fewer sizes are needed to comfortably seal to the range of human face dimensions.
Invert face seal lip. Ready to have filter adapter pressed into opening right off the print bed. In depth directions here: https://github.com/nasa-jpl/COVID-19-respirators/wiki/JPL-Conforming-Respirators