Health
If Your Mask Has a Valve, It’s Half Useless – Lifehacker Australia
If you’re wearing a face mask with a little plastic valve embedded in it, you should know that valves compromise the effectiveness of the mask — and this is true…

If youre wearing a face mask with a little plastic valve embedded in it, you should know that valves compromise the effectiveness of the mask and this is true whether your mask is a hardware-store N95 or a designer cloth mask.
These valves allow exhaled breath to bypass the filter. When you breathe in, the air you breathe is being filtered by the mask; when you breathe out, it is not. (The valve only operates in one direction.)
This video from government agency NIST shows how unfiltered air spews…
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