Tuesday, August 18, 2020

COVID 19 mask: Why do some face masks have valves? Are they more effective?



COVID-19 has markedly changed society over the last four months, with most public interactions taking place between people clad in masks and at a distance. Why do some face masks have valves, and are they more effective?

from Daily Express :: Health Feed https://bit.ly/2Q1SLIt
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