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Materials

What fabrics make the most effective homemade masks?

Scientists test various kinds of cloth for their ability to filter aerosols

by Bethany Halford
May 9, 2020 | APPEARED IN VOLUME 98, ISSUE 18

 

09818-scicon9-masks.jpg
Credit: Shutterstock
Some fabrics are better than others for filtering aerosols.

Tightly woven cotton, such as that used to make high-thread-count sheets; four layers of silk; and mixtures of fabric, such as cotton and flannel or cotton and chiffon, are good materials for making masks to prevent the spread of the novel coronavirus, SARS-CoV-2, scientists report. According to a new study, masks made from these fabrics are good at filtering saltwater aerosols 10 nm to 6 µm—the same size as droplets that are known to spread respiratory viruses (ACS Nano 2020, DOI: 10.1021/acsnano.0c03252). Droplets this size tend to stay suspended in air. Last month, upon learning the Centers for Disease Control and Prevention would recommend that people wear face coverings, scientists at the Pritzker School of Molecular Engineering, the University of Chicago, and Argonne National Laboratory decided to test the filtration properties of various fabrics. “There was very little scientific data taken with laboratory-grade instruments on this,” says Supratik Guha, who led the research. Guha built an apparatus to flow aerosols through fabric and paired it with sophisticated equipment from Argonne that measures the size and distribution of aerosols. After observing which aerosols penetrate 15 types of fabrics, Guha recommends using at least two layers of fabric but not so many layers that airflow becomes blocked. Also, he says, gaps between the contours of the mask and the face can significantly degrade a mask’s performance.

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Comments
Paolo Ciambelli, Professor emeritus University of Salerno (May 13, 2020 1:06 PM)
I appreciated the paper, as it is a rare example of approaching the problem of cloth mask performance, giving some information of fabric characteristics. I agree with the comment on the lack of scientific data, as shown by relevant bibliography. Since there isn't any intrinsic inferiority of natural fibers (even if larger than PP) I think that this subject could be an opportunity for gathering different competence and expertise, from textile science and technology to filtration operation to mask design, to health protection areas. And not forgetting that respirability and face adhesion are so important as filtering efficiency.
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Susan Stoker (July 10, 2020 1:48 AM)
I agree. Input from textile science and technology, filtration operation and mask design are all areas that should comment / add to further expansion of this study. I would like to add one other area of expertise, that of a seamstress. A person with knowledge about readily available sewing materials and how they are used would be helpful when providing information on the fabric used in the study.
After I read this article, 3 questions came to mind.
1. I noticed the study did not consider "interfacing" which many mask-makers use when making the masks. Interfacing is typically used as a stabilizer in sewing. The interfacing is ironed on to the cotton and is meant to help act as a filter. The combination of the non-woven interfacing with 2 layers of cotton fabric is quite common, in mask-making circles. Please note that there are several "weights" of interfacing, from feather weight to heavy weight, to batting. I initially used mid-weight interfacing, but switched to featherweight due to the summer heat.
2. Another question related to how long the various materials would continue to be functional. Cotton retains moisture, silk and wool tend to "whisk" it away from the skin. Understanding that as fabric becomes moist, the filtration lessens, how often would a person have to change an all cotton mask vs a cotton-silk mask?
3. Related to fabrics, microfiber materials have become common due to the stretch characteristic of that fabric. However most of microfibers are synthetic, aren't they? I am curious if a combination of cotton on the inside with the microfiber on the outside is a possibility. The biggest advantage of the microfiber is that it stretches over the contours of the face.

Julie (May 15, 2020 1:19 PM)
There are only 4 types of fabric mentioned in the article. What are the other 11?
Bethany Halford (May 18, 2020 9:52 AM)
Hi Julie,

If you click on the link to the paper, there is a table there with all the fabrics they tested and how well they work filtering aerosols >300 nm and <300 nm.
Ellen (May 27, 2020 11:17 AM)
Bethany where do I click to check out the table with all the fabrics they tested and rated?
Bethany Halford (May 28, 2020 7:14 AM)
Hi Ellen,

The key results can be found in Table 1 if you click on highlighted area that says 10.1021/acsnano.0c03252. There is more information on fabrics in the tables in the Supplementary Information.

Hope that helps.
Mitony (May 29, 2020 4:02 AM)
Pure fabric does not help to filter particles, germs etc... what you need is at least a filter.
Filter is easy to locate on Amazon. But I found something new, its called nano masks, you can search nayi nano mask on FB.

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