My mind was rather blown when I read on the CDC site about the last resort of DIY masks. Scroll down to very last paragraph before the footnotes:
Strategies for Optimizing the Supply of N95 Respirators: Crisis/Alternate Strategies
If that’s the case, please read:
Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? Disaster Medicine and Public Health Preparedness 7(4):413-418 · August 2013
Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?
Then scroll down to the carpenter dude video for instructions:
Ashfall protection: 4 substitutes to N95 mask