While some are still arguing about wearing masks a year after the pandemic, scientists have begun to pinpoint the exact best strategy, and cotton face masks are getting another sign of approval.
Various studies have tested combinations of materials, and health authorities such as the World Health Organization and the Centers for Disease Control (CDC) have recommended cloth masks to the general public, based on their conclusions. But some of these studies omit an important factor in the real world – these fabrics that cover the face end up dampening our breath.
Now, a team of researchers has tested the masks’ materials under conditions of high humidity that mimic the air emanating from our mouths.
“This new study shows that cotton fabrics actually perform better in masks than we thought,” said materials scientist Christopher Zhangmeister, of the US National Institute of Standards and Technology (NIST).
Zhangmeister and colleagues tested 9 different types of cotton and six types of synthetic fibers, including polyester and rayon with a humidity of 99% (about how moist our breath is) and 55% of humidity. This resulted in a noticeable difference in the performance of the cotton.
While synthetic fabrics, which also performed poorly compared to dry cotton, did not change performance under wet conditions, cotton fabrics increased their ability to capture particles by 33%.
The researchers used salt particles of various sizes as a test substitute for droplets and virus-carrying aerosols, and these particles seemed to absorb some of the moisture trapped by the cotton fibers that attract water. The particles swell in size, making it difficult for them to pass through the fabric unimpeded.
However, synthetic fibers repel water and thus do not create a moist environment inside the mask itself for this inhibition to occur. The masks have also remained unchanged – but they are designed to work to high levels in all conditions (levels equivalent to cotton).
Flannel was the best performing cotton, according to the results.
Micrographs of the materials reveal a stark difference in structure – a structured weave pattern in synthetic polyester compared to the chaotic web of cross-linked fibers that give flannel its soft feel.
It is this mess of fibers that increases the chance of airborne particles colliding, which pass through the mask and stick to the fabric, researchers believe at the National Institute of Standards and Technology (NIST).
However, all this does not mean that wet masks are better: if the mask gets wet, it must be replaced. The amount of liquid in the masks in these humid conditions is only a few drops, which does not change the breathability of the material – the team found that the air pressure on both sides of the fabric remained relatively similar.
And that’s great news from an environmental perspective, too. With the buildup of waste from disposable surgical masks that remove microplastic particles, it is comforting to know that there is a safe and reusable option.
Research indicates that having a set of reusable masks that can be washed together in a washing machine is the most environmentally friendly option to keep you and your loved ones safe.
While the team says that more research is needed to fully appreciate the interactions between masks, moisture and the transfer of aerosol particles, their study contributed to setting the first international standards for cloth masks aimed at slowing the spread of “Covid-19”, which were recently released according to international standards ASTM. .
“To understand how these materials perform in the real world, we need to study them under real conditions,” Zhangmeister concluded.
The research is published in ACS Applied Nano Materials.