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Nonwoven masks are best defense, but choose your face covering carefully: Japan expert

A nonwoven cloth mask, which research shows is better at stopping fluid droplets than other types of mask. (Mainichi/Natsuko Ishida)

TOKYO -- More shops and schools across Japan are asking people not just to wear masks, but specifically to wear nonwoven cloth masks. The reason: Research results show that the nonwoven coverings are more effective at stopping droplets than the regular cloth or polyurethane versions that became popular in part due to their looks during last spring's mask shortages. Now, experts are calling on people to choose the best type of mask for the situation, depending on their health and cost performance.

    On Jan. 7, the board of education in Tokyo's Suginami Ward asked all its elementary and junior high school teachers to wear nonwoven cloth masks, even during gym class, as part of a written call for thorough anti-infection measures. The board also announced it was recommending that children wear the masks as well, if possible.

    The recommendation "is based on the opinion of the ward's public health center, and does not mean that we will be forcing children to wear nonwoven masks," the education board explained.

    Meanwhile, a look at facility websites across Japan -- from Tokyo-area gynecology clinics, dentists and clothing stores to hairdressers in Hokkaido and fitness spas in Kyushu -- shows that increasing numbers of them began asking patients and patrons to wear the nonwoven masks this month. Some spots were offering to give the masks to customers, while one hairdresser was selling them for 30 yen (about 29 cents) apiece.

    A facility website displays a request for visitors to wear nonwoven cloth masks.

    Despite all this, polyurethane masks remain very popular, especially among young people. One 32-year-old woman from Ishikawa, Chiba Prefecture, who has been a polyurethane mask devotee since last spring told the Mainichi Shimbun, "I like them because you can wash and reuse them, and you can choose from different colors to coordinate with your outfit. Also, it's easy to get makeup stains on the white nonwoven cloth ones."

    She added, "I'd wear a nonwoven one if I were going to a hospital, but as long as society doesn't look at me too severely, I plan to keep using polyurethane masks most of the time."

    The sudden upswing in nonwoven cloth mask recommendations stems from research by a team including the Japanese government-backed Riken institute, the Toyohashi University of Technology. Running simulations on the Fugaku supercomputer, the team investigated how well different mask types -- nonwoven cloth, regular cloth and polyurethane masks -- stopped droplets. The spread of airborne droplets from the mouth and nose of an infected person is one of the main ways the coronavirus is transmitted.

    The simulation results, released last year, showed that many kinds of nonwoven cloth masks managed to filter out more than 90% of these droplets, but that they were also not very air-permeable. The results for regular cloth masks varied wildly depending on the type of cloth, number of layers and other factors, with some performing as well as their nonwoven cousins.

    In this April 2020 file photo, a "sold out of masks" sign is posted outside a drug store in Hiroshima's Naka Ward. (Mainichi/Tatsuya Fujii)

    Polyurethane masks, on the other hand, only managed to filter out 20-40% of droplets.

    Based on these results, the team tested the masks' effectiveness when actually being worn. As predicted, very few droplets made it through the nonwoven cloth masks, while the polyurethane masks performed relatively poorly.

    However, this does not mean that the research team is issuing a blanket endorsement of nonwoven masks. Put simply, not all of them are equally effective, and there have been some on the market that do a poorer filtering job than regular cloth masks.

    "Basically, the ones that make it harder to breathe are more effective. That's what I'd like people to remember," said Riken research team leader Makoto Tsubokura, a professor at Kobe University. He added, "If you're in a regular office environment, then a cloth mask will do. On days when you're going someplace where you could encounter crowds, then go with the nonwoven cloth mask. In other words, choose your mask based on your physical condition and the infection risk associated with where you're going."

    Nonwoven cloth masks are, as the name suggests, made from non-fabric fibers, bonded together or enmeshed using heat, chemical or mechanical processes to create thin cloth sheets.

    (Japanese original by Shuji Ozaki, Tokyo Regional News Department)

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