Nice job, hats off for coming up with a solid design. One thing: masks with exhalation valves should probably not be used by people who infected and shedding virus, since the valve just lets the droplets fly out of the mask. These would be more appropriate for caregivers and the general public, I'd think.

Yes you totally right. Thanks for your feedback. We are planing to design more models without valves just like 3M surgical masks and make them easy to build with replacable.