While some still argue with the use of masks a year after the pandemic, scientists have followed exactly which strategy is best and cotton masks have just received another approval.
Several studies have tested different combinations of materials and health authorities such as the World Health Organization and the CDC recommend cloth masks to the general public, according to their findings. But some of these studies overlooked an important real-world factor: these face-covering tissues end up wet from breathing.
Now, a team of researchers has tested mask materials in high-humidity conditions that mimic the air expelled from our mouths.
“This new study shows that cotton fabrics actually work better on masks than we thought,” said materials scientist Christopher Zangmeister of the U.S. National Institute of Standards and Technology (NIST).
Zangmeister and colleagues tested nine different types of cotton and six types of synthetic fibers, including polyester and rayon, with 99 percent moisture (approximately breath moisture) and 55 percent d ‘humidity.
This resulted in a noticeable difference in cotton yield.
Cotton masks become better filters when they absorb moisture from the breath, which makes them even better by slowing down COVID-19 than we thought: https://t.co/qbGtnC4a42 pic.twitter.com/91hNVIvlTX
– National Institute of Standards and Technology (@NIST) March 9, 2021
Although synthetic fabrics, which also malfunctioned compared to dry cotton, did not change performance in wet conditions, cotton fabrics increased its ability to capture particles by 33%.
The researchers used salt particles of different sizes as a substitute for the particles of droplets and aerosols that carried viruses, and appeared to absorb some of the moisture trapped by the cotton fibers that attract water. The particles swell in volume, making it harder for them to pass uninhibited through the tissue.
However, synthetic fibers repel water and therefore do not create the moist environment within the mask itself for this inhibition to occur. There were no changes to the medical masks either, but they are designed to work at high levels in all conditions (levels equivalent to cotton).
According to the results, the cotton with the best performance was cotton flannel.
Microscopic images of the materials reveal a strong structural difference: an orderly pattern of fabric made of synthetic polyester compared to the chaotic network of interwoven fibers that give the strip its soft-touch feel.
NIST researchers believe that this fiber mess is what increases the chance of airborne particles passing through the mask colliding and adhering to the fabric.
Cotton flannel (left), polyester (right). (EP Vicenzi / Smithsonian Museum / NIST)
However, all this does not mean that wet masks are better: if the mask gets wet, it should be replaced. The amount of liquid present in the masks in these humid conditions amounts to only a few drops, which does not alter the transpiration of the material; the team found that the air pressure on either side of the tissue remained relatively similar.
They are also good news from an environmental point of view. With the assembly of waste disposable surgical masks that dispose of microplastics, it is comforting to know that there is a safe and reusable option.
Research suggests that owning lots of reusable machine washable masks is the most environmentally friendly option to protect you and your loved ones.
Although the team says more research is needed to fully appreciate the interactions between masks, moisture, and aerosol particle transmission, their study has contributed to the first international standards for fabric masks designed to curb spread of COVID-19, recently published by the standards -organizing organization ASTM International.
“To understand the performance of these materials in the real world, we need to study them in realistic conditions,” Zangmeister concluded.
This research was published in Dwarf materials applied by ACS.