Recent studies show that valved respirators are actually better than or equivalent to surgical and cloth masks for source control: https://www.cdc.gov/niosh/do

Recent studies show that valved respirators are actually better than or equivalent to surgical and cloth masks for source control: https://www.cdc.gov/niosh/docs/2021-107/default.html https://www.cdc.gov/niosh/docs/2021-107/default.html However, the "valves bad" mantra has been repeated so long and so strongly that it is unlikely there will be any official guideline change.