It is now completely clear that face masks are an important and effective tool in preventing the spread of COVID-19. In a new study, researchers found a way to test the effectiveness of different types of face masks – and found that not all of them are equally effective at actually catching the breath droplets that may contain the virus.
For the study, published last week in Advances in science, The researchers developed a simple, inexpensive way to test different types of face masks. The testing method requires someone wearing a face mask to speak into a box with a laser inside. The beam from the laser is perpendicular to the direction of the particles coming out of the person̵
Researchers tested their design by using it to study the effectiveness of 14 different types of face masks, including basic surgical masks, customized N95 masks, cotton masks, knitted masks, and bandanas. During the test, the speaker repeated the phrase, “Stay healthy, people” five times without shouting. The process was repeated 10 times for each mask. And for the masks that allowed more particles to escape, the researchers ran additional tests on air from a lightbulb to make sure the particles weren’t just dust from the mask, but actual droplets coming from the Speakers were ejected.
Perhaps unsurprisingly, the custom N95 masks showed the best when tested, meaning they let the fewest droplets pass through. The second most effective masks were simple three-layer surgical masks that appear weak but are precisely designed to reduce the transfer of such droplets. Next came masks that those of us who aren’t in the medical profession are more likely to wear, including masks made from a combination of cotton and polypropylene (a material derived from plastic), two-layer polypropylene masks, and two-layer folded cotton masks.
However, as the masks become less effective, the data also becomes cloudy. The lower masks were knit masks, bandanas, and fleece (defined as “gaiter-type running fleece”), all of which appeared to be about as ineffective as if they were not wearing a mask at all. However, when looking at the actual results, the effectiveness of these masks was much more variable. Therefore, it is difficult to say whether one is really the worst or whether they are all equally bad in this particular test.
There were a few other issues with the study as well that the researchers noted. For example, the test device only measured the droplets that came from a small portion of the space directly in front of the speaker’s mouth. The amount of droplets released from the sides of the mask was not measured. The study also used only a few different speakers at a set volume to test the masks, so you may see different results from different people or from people shouting, singing, or coughing. Therefore, these results should not be taken as a final ranking of what to wear and what not.
However, in general, these results agree with what we already know about the best face masks. We know, for example, that N95 masks are the best at preventing the spread of breath droplets. We also know that in the absence of N95, surgical masks are a good option, but they are also not reusable. And when it comes to reusable cloth masks, we know that a tight fit, multiple layers of material (including cotton), and wearing the mask in the correct position can go a long way towards making a mask effective.