[Goose]

One thing I am seeing a lot of are masks with valves on them. This can make it easier for people to exhale, but it obviates some of the purpose of the mask to trap your own respiratory secretions. I think most of them are manufactured that way because it makes them seem more premium to an unknowledgeable consumer. 

I believe they are manufactured that way because they are designed to use in construction and factory settings where there is lots of particulate matter contamination that needs to be excluded from inhalation. Exhalation needs to be as easy as possible, as in this setting there is no requirement to filter the exhaled air.

[Goose]

One thing I am seeing a lot of are masks with valves on them. This can make it easier for people to exhale, but it obviates some of the purpose of the mask to trap your own respiratory secretions. I think most of them are manufactured that way because it makes them seem more premium to an unknowledgeable consumer. 

I believe they are manufactured that way because they are designed to use in construction and factory settings where there is lots of particulate matter contamination that needs to be excluded from inhalation. Exhalation needs to be as easy as possible, as in this setting there is no requirement to filter the exhaled air.