Most people are making do it yourself (DIY) face masks at home with cotton and may also be adding tissue or a paper towel. There may be a problems with this. These materials very quickly absorb water - for example, a droplet from a cough or a sneeze. The water droplet rapidly penetrates the material and makes its way to the inside of the mask where you are breathing.
N95 respirators, according to the CDC, "are tested for fluid resistance, filtration efficiency (particulate filtration efficiency and bacterial filtration efficiency), flammability and biocompatibility."
I believe fluid resistance is the key word. For the coronavirus traveling in a tiny water droplet, you want the mask to repel water so the droplet sits on the surface and evaporates. Then the virus presumably remains on the outside of the mask.
Watch this video of an experiment I did to improve the "fluid resistance" of any mask you may make at home, or otherwise acquire and use.
I did not do enough testing to prove that the more hydrophobic (water repelling) mask will provide more protection, but it certainly makes sense.
If you don't have access to testing, your next best action is to take any of these surveys:
Free 10 minute COVID-19 consults are now available. Write to me at email@example.com and provide your phone number. I cannot go beyond 10 minutes however.
Thomas J. Lewis, Ph.D.