[jonrick46]

This scientific study say face masks can be made effective:

“In summary, we find that the use of cloth masks can potentially provide significant protection against the transmission of particles in the aerosol size range.”

https://pubs.acs.org/doi/10.1021/acsnano.0c03252

[norcal joe]

This scientific study say face masks can be made effective:

Yes, they were able to show that cloth masks can "potentially" provide significant protection, but using hybrid materials, and also noting that a significant reduction in effectiveness is seen around the edges of the masks. I'm somewhat skeptical that this is practical for mass populations.

[Grandpa Drudge]

Your referenced scientific study describes what the masks are and how well they work, and measures their effectiveness at filtering particles. Particle sizes tested were >5 um and <5 um. Note that virus aerosol particles are <2.5 um, (and most are about 1 um) too small for these masks to filter out.

From your referenced scientific study: The N95 mask (best one available) is 85% effective for <5 um particles when perfectly fitted (no gap) and only 34% effective (with gap). The cheaper surgical mask is 76% effective when perfectly fitted (no gap) and 50% effective (with gap).

Because virus aerosol particles are smaller than 5 um (as small as 1 um) it is obvious why these masks will NOT prevent aerosol infection by Covid-19.

That's probably why the scientific studies reviewed by Dr. Denis G Rancourt, PhD all discovered that neither surgical masks or N95 masks were effective in Preventing transmission of viruses.