[gibba999]

The best source I've seen are the tracing studies in China. Police state meant China could follow exact paths -- from camera footage -- of who caught COVID from whom. If both sides wore surgical masks (imperfect fit, but electrostatic layer), there was almost never any spread.

Singapore hospitals were good case studies too. Hundreds of COVID19 exposures early in the pandemic, with virtually no spread.

You can do web searches for both.

Million dollar question is how this impacts delta. Delta has higher viral loads, and it's perfectly possible filtering 95% of delta will still result in more virus than the original, unmasked. Things also get more complex with both sides filtering; naive math would place filtration at 99.75% effective, but I don't believe naive math in this case beyond saying "a lot more effective."