But if old masks must be reused my guess is that they could be exposed to UV light, (UV from sun highest near noon) sprayed with alcohol and allowed to dry, or heated to a temperature just below where the elastic breaks down.
Masks are most valuable to put on sick people, including sick people who do not yet feel they are sick.
Since there is a 4 to 10 day incubation period before symptoms are felt when you wear a mask in public you are mainly doing a great favor to other people.
Masks do reduce by about a 1/3 your chances of breathing in a relatively fat water droplet that was coughed/sneezed out from a sick person.
In low humidity fat droplets evaporate away to small droplets that can go through masks. This is a time to hope for high humidity to come early.
In high humidity warm weather fat droplets stay fat much longer because evaporation is much less and these fat droplets sink faster to the ground where the virus fairly quickly becomes inactive.
