Grace Tsiang point us to a quite recent a comparison of medical masks worldwide. She adds:
I think that as economists, we should remind policy makers (such as WHO) that testing facemasks in in clinical settings will always miss the substantial shift in behavior when consumers are given a “gift” of advanced technology pushing a production possibilities frontier outward. Consider substitution by consumers towards more fun activities when the safety of those actions are reduced. That substitution affects the new cool tech’s EFFECTIVENESS in use. The fancier the construction & materials, the lower is the incentive to avoid risky behaviors.
Simple cloth masks function far better in life than in clinical comparisons, because they are first and foremost Reminders to use best practices. All the desired practices, such as avoidance of going out in company while sneezing/coughing, handwashing after contact with other people or communally touched surfaces, and other cleaning practices remain very costly with mere cloth than some (overly?) trusted and possibly incorrectly used higher tech respirator.