If it doesn't filter the exhale, you're spreading to others. Especially if you're asymptomatic. That's one reason why many places (correctly) forbid masks with valves.
> That's one reason why many places (correctly) forbid masks with valves.
No wrong. The CDC has written guidelines here in favor of exhalation valves on N95 masks (which are filtered), the guidelines specifically recommend against not forbidding such masks if they are NIOSH-approved N95 ones:
My N95 filtering facepiece respirator has an exhalation valve. Is that ok? Will it protect both me and others?
Yes, an N95 filtering facepiece respirator will protect you and provide source control to protect others. A NIOSH-approved N95 filtering facepiece respirator with an exhalation valve offers the same protection to the wearer as one that does not have a valve. As source control, findings from NIOSH research suggest that, even without covering the valve, N95 respirators with exhalation valves provide the same or better source control than surgical masks, procedure masks, cloth masks, or fabric coverings. In general, individuals wearing NIOSH-approved N95s with an exhalation valve should not be asked to use one without an exhalation valve or to cover it with a face covering or mask. However, NIOSH-approved N95 respirators with an exhalation valve are not fluid resistant. Therefore, in situations where a fluid resistant respirator is indicated (e.g., in surgical settings), individuals should wear a surgical N95 or, if a surgical N95 is not available, cover their respirator with a surgical mask or a face shield. Be careful not to compromise the fit of the respirator when placing a facemask over the respirator.
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Many countries will require N95 masks (many of which have valves, so that is acceptable). So on a plane from Amsterdam to Beijing, you might have to switch masks during the flight (because the Dutch, for reasons, don't allow valves in favor of less effective cloth/surgical masks, while the Chinese...for reasons, require N95 masks that might have valves).
I am indeed wrong. Thanks for the details and the link. I hadn't checked in on the valve recommendations since early in the pandemic. I'd edit my above if I could.