Finding the Best Mask Material for COVID-19 Protection

As we continue to fight against COVID-19 and other airborne viruses, people are turning to reusable cloth masks to protect themselves. But what is the best material to use? A new study shows that the fabric you choose may make or break how well your mask works. The research, published in ACS Nano this week, shows that tightly woven cotton and fabrics that hold electrostatic charges like certain types of chiffon and natural silk can go some way to stopping the spread of the virus by filtering droplets. The findings could have a significant impact on how we respond to future pandemics.

Previous studies have shown that a mask's effectiveness depends on both the shape of the fabric and its chemical properties. The researchers compared different types of fabric and found that the best combination of materials for masks is three layers, with a layer of tightly woven cotton or linen as the outer shell, an inner absorbent layer of cotton or polyester, and a layer of non-woven spunbond polypropylene (which is similar to what's used in medical masks) as the filter. The best masks were also those that clung closely to the face. This helped prevent the release of virus particles into the air, as well as limiting the transmission of the disease through contact.

The researchers found that the most effective masks filtered 99 percent of COVID-19 droplets when using a sample from a patient with severe acute respiratory syndrome coronavirus type 2 infection, or SARS-CoV-2. The research team also found that repeated washing of a mask doesn't degrade its ability to filter droplets—in fact, the researchers suggest that the fabric might get even more effective over time, due to pore shrinkage. The study's authors plan to continue testing a variety of fabric combinations and shapes.

Other factors that can help or hinder a mask's efficiency include the thickness of the fabric and its water resistance. The researchers tested a number of different types of fabrics and thicknesses of the inner and outer layers, but they recommend a heavier, more tightly woven cotton or cotton-polyester blend. Tightly woven fabrics will keep their structure better and be less likely to rip or tear, which can open up gaps in the filter.

A final consideration is whether the mask can be worn and washed repeatedly. The best masks had a layer of NWPP that was machine washable and sterilizeable, but could be laundered or washed separately from the rest of the mask. The researchers also recommend avoiding synthetic fabrics, such as polyester and nylon, which don't breathe as easily and can cause moisture to form that may interfere with the mask's ability to filter.

Alternatively, the researchers suggest that users who want to make their own masks can try two sheets of tissue paper folded into a four-layer filter. This approach, which would work just as well as a mask made of non-woven spunbond polypropylene, is cheap, easy to come by and can be easily stored in your bag for quick emergency use.