Although respirators with one-way exhalation valves can make wearing a mask more comfortable, their use as a way to prevent the spread of COVID-19 in public has been discouraged. The thinking is that valves do not effectively filter particles as exhaled air passes through them, but few studies actually have looked at this. Now, researchers report in ACS’ Environmental Science & Technology Letters that one valved N95 mask performed substantially better than another.

Face coverings filter out particles, helping decrease the transmission of respiratory diseases. And as COVID-19 community levels shift, masks will still be needed in some settings. But previous studies haven’t provided clear guidance on how valved respirators impact the spread of exhaled particles. Either the sample size has been very low—in one instance, only a couple of people wore one brand of valved mask—or they have been performed under idealistic wearing conditions. So, Christopher Cappa and Jessica Hazard wanted to know what would happen if 10 volunteers spoke while wearing different mask types, including two different valved respirators. Cappa and Hazard also asked the volunteers to wear the coverings as they would in the real world.

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