NBC新闻:新研究揭示不同口罩防护效果

These days the choice of face masks can be dizzying. So researchers at Duke Health set out to find which may work best, testing 14 different types with a simple experiment designed to visualize small particles or droplets sprayed during regular speech. Researchers said the same phrase. Stay healthy, people. First with no mask, note the flashes of light. Those are the tiny particles which could contain coronavirus. If everyone wore a mask that truly blocked these particles, we would reduce the spread of a transmissible disease like covid-19. No question about it. 

Medical grade N95s and surgical masks both worked well to block particles. But masks with exhalation valves won't protect those around you. Cotton masks with several layers of material did well, not a lot of droplets got through. You don't need a perfect mask to reduce community spread. But bandanas and neck gaiters didn't fare well. In fact, researchers say they may result in more small particles than no mask at all. Bottom line, Lester, researchers say masks work if they have several layers of good fabric. If you can see through it, it's probably not doing you much good.