27 APRIL 2020
With the CDC recommending surgical and N95 masks should be kept for medical personnel on the front line, if you do want or need a mask, you should be purchasing or making a cloth one.
But when looking at cloth masks, which materials work best for keeping your germs in and other people’s germs out?
Researchers from the Argonne National Laboratory and the University of Chicago in the United States have taken a variety of common materials and tested them in laboratory conditions – investigating their mechanical and electrostatic filtration properties.
The team found that multiple layers and mixing up fabrics worked best to filter particles, but improper mask fit can ruin the whole thing.
“We have carried out these studies for several common fabrics including cotton, silk, chiffon, flannel, various synthetics, and their combinations,” the researchers explain in their new paper.
“Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.”
(Konda et al., ACS Nano, 2020)
Creating the pretty intense experimental set up illustrated above, the team used an aerosol mixing chamber to sample the number of aerosols in the air. They then passed the particles though each of the test fabrics (which were tightly secured on the end of a PVC tube) and sampled the air that made it through the material.
They tested for a large range of particle sizes, from around 10 nanometres up to 10 micrometres. To put that in perspective a human hair is approximately 50 micrometres in diameter, and there’s 1000 nanometres in a micrometre. Coronavirus particles are between 80 and 120 nanometres in diameter.
So, the particles tested were tiny – and there’s still some debate on whether these tiny aerosolised particles can even cause infection, but if you’re getting the little particles you’re definitely getting the big ones. So making sure materials can filter out the smallest scale is a good way to ensure the larger particles will be blocked.
The team found that ‘hybrid’ fabrics (aka layering multiple materials) were able to filter the vast majority of particles.
“Filtration efficiencies of the hybrids (such as cotton–silk, cotton–chiffon, cotton–flannel) was >80 percent (for particles <300 nanometres) and >90 percent (for particles >300 nanometres),” the researchers write.
“We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mechanical and electrostatic-based filtration.”
Mechanical filtration is just the fabric physically catching the particles – the team found that with fabrics such as cotton, high thread count works the best. The smaller the holes, the fewer large particles can escape.
Electrostatic-based filtration is a little different. Think of a super static-y material such as polyester. Instead of zapping a friend with all the static electricity you saved up, the electrostatic filter keeps the aerosols inside the static environment.
But this all comes to nothing if you don’t wear your mask correctly. In the second half of the experiment the team poked small holes in the fabrics they were testing, and the results were not pretty.
“Our studies also imply that gaps (as caused by an improper fit of the mask) can result in over a 60 percent decrease in the filtration efficiency,” the researchers explained.
So, whatever you make your mask out of, make sure to wear them properly.
If you want to find out how to actually make the mask out of your new hybrid fabrics, we recommend checking out the many tutorials online.
And if you need something a bit simpler with the items you have at home, the CDC has you covered.
The research has been published in ACS Nano.