I think the single study that supported cloth face coverings of no particular standard of performance was a mechanistic study that depends on the belief that respiratory illness spread is a direct function of the distance water droplets of an arbitrary threshold size travel from a simulated sneeze. Which, of course, is so obviously true it needs no supporting evidence.
https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article
I think the single study that supported cloth face coverings of no particular standard of performance was a mechanistic study that depends on the belief that respiratory illness spread is a direct function of the distance water droplets of an arbitrary threshold size travel from a simulated sneeze. Which, of course, is so obviously true it needs no supporting evidence.