A new study led by the US government found that common materials like cotton can effectively filter out particles as small as coronavirus, especially in layers. The findings offer more evidence that homemade masks can slow the spread of the pandemic and possibly provide some personal protection against covid-19, although not as much as you would get with medical-grade respirators.
Their become obvious that wearing masks can reduce the spread of the coronavirus in the general population. At the very least, masks can block some of the larger drops containing viral particles that a person exhales or coughs, preventing them from reaching others. The widespread use of masks is important, because people can be contagious without feeling sick or shortly before symptoms begin.
But there are still questions about how effective different types of masks are, including homemade cloth masks, and whether they are of any use in preventing other people from infecting people. Breathing masks, like the N95, are specifically designed to filter out potentially infectious aerosols and prevent infection.
The new study was published This month at ACS Nano and involved researchers from the National Institute of Standards and Technology (NIST), as well as from the Smithsonian Institution Museum Conservation Institute.
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They conducted simple experiments with 32 different types of fabrics made from cotton, wool, and synthetic fibers. Large and small particles were dumped into samples of a fabric, and then the researchers measured how many particles were not captured by the fabric and remained in the air. However, instead of using live coronaviruses, they used table salt particles, which are similar in size to the viral particles we exhaled.
In the end, it was clear that cotton fabrics were the best on average to block coronavirus-sized particles, compared to synthetic fabrics. But not all cotton fabrics were created equal. Cotton that had high layers, like the type you’d see on flannel, worked better than other types of fabric. The tighter a fabric was, the better it performed.
“Texture turned out to be one of the most useful parameters to look at because we found that most high thread count cotton fabrics tend to filter better,” said study author and NIST researcher Jamie Weaver in a Press release from the agency “Our findings suggest that a fabric’s ability to filter particles is based on a complex interaction between material type, fiber and fabric structures, and thread count.”
The researchers also found evidence that stacking multiple layers of fabric would further increase the effectiveness of cotton masks. But more importantly, they also discovered that even the best homemade masks that fit someone’s face perfectly probably won’t provide as much protection against infections as an N95 mask. The best single-layer cotton blocked approximately 20 percent of the particles in the virus range, while the N95 masks are designed to block 95 percent of particles of that size, as the name implies. Some cotton fabrics that were shown to be more effective at blocking virus-sized particles would also be more difficult to breathe, highlighting a possible tradeoff between safety and accessibility.
“The bottom line is that none of these fabrics is as good as an N95 mask. Still, fabric overlays can help slow the spread of the coronavirus, ”said study author and NIST research fellow Christopher Zangmeister. “We hope this research will help DIY manufacturers and hobbyists determine the best fabrics for the job and serve as the basis for further research.”
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