This device is a general purpose face mask intended for use in the community and is not suitable for use by a healthcare professional or in a healthcare facility or environment, as described in FDA Guidance Enforcement Policy for Face Masks and Respirators During the Coronavirus Disease (COVID-19) Public Health Emergency, Section V B.  This device has not been tested to assess the out-gassing limits of the material or their corresponding health effects.

This is my design for a re-usable face mask frame that could utilize a variety of filter media. This is NOT a respirator and does not claim to be, however, many design features were inspired by respirators. I welcome all feedback in the comments section to further iterate and optimize.

It consists of the following:

• A flexible liner from TPU/TPE designed to roll inward and conform to the face. In doing so it creates a much better seal than rigid shells and folded TPU sheet style designs. However, it won't be able to match super soft medical-grade silicone. Print with four top layers, 0% infill, and zero bottom layers for best results.
• Rigid shell onto which everything mounts. The lip is intentionally oversized to create a seal between the liner and the shell. Grills require a printer capable of bridging 8mm.
• The gasket/flap piece combining two functions to reduce complexity and parts count
• Filter media. Depends on what's locally available. I've tested this design with vacuum cleaner bags, cloth, and one third of a surgical mask.
• The cover piece applies pressure to the gasket and forces the valve flaps against the exhaust openings. It also ducts exhaust to the rear. It should be printed in 100%TPU.
• Strap mounts designed to be modified for different configurations. They snap in place once the cover is added.  v5.2 is the latest.
• Straps - Refer to images to see the current configuration.  I used 550 cord sheath pieces of 1m, 500mm, and 500mm.  Create a loop in the 1m piece tied off with a square knot.  Attach the shorter pieces to the loop via lark's head knots.  Secure via the strap fitting part, adjust tension, and trim excess.

The usual caveats about printing this sort of device apply as testing has been limited. But all plastics used during prototyping survived my local hospital's H2O2 atomizing autoclave device, so it can be sterilized. My excellent medical provider and the local medical engineering team will continue to conduct further testing on plastics used to include more field expedient methods of sanitizing, porosity/liquid absorption, and oxygen flow/CO2 build-up with different filter media (though the one-way valves should help with the last). I also want to coordinate for a vapor spectrometer test to see if the printing process releases and VOCs in printed samples.  The AMF files should offer a complete set, since NIH decided to no longer allow STL uploads.

I think this is about as complicated and feature-packed as one can go for a face mask producible on a consumer-grade printer using commonly available filaments. It requires about 6H total to print all parts, so production is not as scalable as I would prefer though it might present an interesting exercise in distributed manufacturing.

And of course, safety considerations:
-Use this design at your own risk...something something neither liable nor responsible...something something...
-3D printed items can be porous and permeable
-Recommend checking the SDS of whatever you print for particulates and hazardous volatile compounds
-This will be an inferior/less desirable solution than similar parts from approved sources
-Pretend that you have COVID-19 when moving the part from the print bed to a sealed container for delivery
-I fly helicopters and ride motorcycles, so my perception of acceptable risk likely doesn't match yours or the FDA's.
-Also, properly washing your hands for 20s and practicing disciplined social isolation will almost assuredly do more to improve your health outcomes than any mask you can buy or print. Don't risk compensate.

Special thanks to Dr. Connor, Mr. Saesz of O2 Canada, the CCDC, ONR Tech Solutions, AFFOA, and the S&T Team for input and ongoing evaluation of this design.