The FDA has authorized production of  face masks outside of the normal clearance pathway during the Covid-19 pandemic, based on Part 5, section D of the “Enforcement Policy for Face Masks and Respirators During the Coronavirus Disease (COVID-19) Public Health Emergency Guidance for Industry and Food and Drug Administration Staff.”

This model can be used to house self-made activated charcoal filters by using cotton pads and activated charcoal. The charcoal is held in place by the clamp part applying pressure on the rim. Alternatively, a HEPA filter can also be used in this design. The filter cartridge design enables pre-build to easily swap in new filters without having to disassemble the filter itself. I have personally print tested this to make sure the threads interface correctly. Although not required, I recommend a bead of silicone on the portion that interface's with the subject's face for better sealing and comfort. Please see the attached images for the filter assembly instructions.