The scientific comparison of masks materials

As states and countries continue to lift some prohibitions on coronavirus and millions decide whether to venture outdoors, it has been widely adopted to wear a mask or face covering.

The N95 masks should be worn by frontline medical staff, public health officials suggest. But what's the best material for protecting yourself and others around you if you're going to buy a traditional mask or make your own out of cloth?

To decide what kind of mask material is most effective in trapping ultrafine particles that could contain viruses such as SARS-CoV-2, the virus that causes COVID-19, a team of researchers tested everything from t-shirts and socks to jeans and vacuum bags.

The researchers from the University of Cambridge and Northwestern University tested the efficacy of various fabrics at high speeds, equivalent to coughing or heavy breathing, to filter particles between 0.02 and 0.1 micrometers, around the size of most viruses. N95 and surgical masks, which are more widely used in healthcare environments, have also been checked.

Previous experiments have looked at a limited variety of fabrics as the wearer usually breathes, as particles are expelled at a lower velocity. A more comprehensive evidence base for the efficacy of fabric masks is provided by researching more fabrics and testing them at higher speeds.

The findings, published in the BMJ Open journal, show that the majority of fabrics widely used for non-clinical face masks are efficient in filtering ultrafine particles. Although a reusable HEPA vacuum bag actually surpassed the N95 efficiency in certain respects, N95 masks were highly effective.

As for homemade masks, those made of multiple layers of fabric were more effective, and a major improvement in performance was shown by those that also incorporated interfacing, which is usually used to stiffen collars. However, this performance boost also made it more difficult for them than an N95 mask to breathe through.

When wet, and after they had gone through a standard washing and drying cycle, the researchers also tested the efficiency of various fabrics. They found that after one laundry cycle, the fabrics performed well when damp and worked sufficiently, but previous studies have shown that repeated washing degrades the fabrics, and the researchers warn that masks should not be indefinitely reused.

Although there are numerous online places that help individuals build their own masks, there is no scientific proof of what the most acceptable materials are.

"O'Kelly said," There was an initial panic about PPE and other forms of face masks, and how successful they were. " As an engineer, I wanted to learn more about them, how well different materials worked in various conditions, and what made the most successful match."

O'Kelly and her colleagues designed an apparatus consisting of parts of tubing for the current analysis, with a fabric sample in the center. At one end of the apparatus, aerosolized particles were produced and their levels were measured at a pace comparable to coughing before and after passing through the fabric sample. The researchers also measured, based on qualitative input from users, how well each fabric worked in terms of breathing resistance.

"A mask that blocks particles very well but restricts your breathing is not an effective mask,” O'Kelly said. “Denim has been very effective at blocking particles, but it's hard to breathe through, so it's probably not a good idea to make an old pair of jeans out of a mask. N95 masks are much easier to breathe through than any mix of fabrics with similar filtration levels."

The researchers consulted with online sewing groups in preparation for the study to find out what types of fabric they were using to make masks. Some of the sewers indicated that they were experimenting with inserting vacuum bags with HEPA filters into masks due to the extreme shortage of N95 masks at the time.

The researchers found that single-use and reusable vacuum bags were effective in blocking particles, but they were careful not to use single-use bags in face masks because they break apart when cut and can contain material components that are dangerous to inhale.

The researchers warn that their research has many limitations: namely, they did not look at the role that fit plays in particle filtering. In a similar project, O'Kelly researched how it is possible to improve the fit of masks in healthcare settings. Furthermore, several viruses are borne on droplets that are larger than those studied in the present analysis.

However, when selecting which fabric to use for making masks, O'Kelly says the findings may be useful for sewers and manufacturers. "In an emergency situation where N95 masks are not available, such as in the early days of this pandemic, we have shown that fabric masks are surprisingly effective in filtering particles that can contain viruses even at high speeds."

'Hybrid' fabrics is the best material according to few scientists:

The research team found that in order to filter coronavirus particles, several layers and mixed up fabrics performed best. But it can ruin the whole thing if the mask isn't the best match. In their new paper, they clarified that they performed their experiments on traditional fabrics such as cotton, silk, chiffon, flannel, different synthetics, and their combinations.

In order to sample the number of aerosols in the air, the research team used an aerosol mixing chamber. They then passed the particles through each of the sample fabrics after mixing the aerosol, which is secured at the end of the PVC tube, and tested the air that went through the material.

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