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Infectious Diseases

14 July 2020

Here are the best and worst materials for face masks

As the WHO is considering evidence that Covid-19 is more airborne than previously thought, masks are even more vital … but which fabrics are most effective?

  • With increasing evidence of airborne Covid-19, wearing masks is more important than ever
  • There are many kinds of fabric masks available, but they don't all have the same filtering abilities
  • Exposure to airborne droplets hugely increases your infection risk

As more scientists are presenting evidence that SARS-CoV-2 is airborne and tends to spread, especially in indoor areas, masks are becoming a mandatory protective measure on airplanes, trains and in shared office areas.

But which masks perform the best? As the pandemic progresses, we're seeing several designs of non-medical masks. But, before you waste your money on useless masks, researchers have determined which ones are the most effective.

Infection risks reduced on several levels

According to a press release, a recent study on masks by the University of Arizona was published in the Journal of Hospital Infection. This research assessed the shielding ability of several types of non-medical mask materials after 30 seconds, and then after 20 minutes of exposure in an area with high contamination risk. 

The study found that infection risks were reduced by 24–94% up to 44–99%, depending on the type of mask and the length of exposure. The shorter the exposure, the lower the risk.

So, what are the best types of masks?

The researchers ranked the mask types as follows:

1. N99 masks

N99 masks, which are one of the best options for blocking the virus, can reduce your average infection risk by 94–99% for 30-second or 20-minute exposure windows. Unfortunately, these masks can be expensive and there is the ethical consideration that we should rather be reserving them for health workers on the front lines.

2. N95 masks, surgical masks, or masks with filters

N95 masks, surgical masks and masks with a built-in vacuum filter were the next best option. Once again, it's vital that healthcare workers have preferential access to these masks. Surgical masks cannot be reused and need to be discarded after a single use. The vacuum filters reduced infection risk by 83% in a 30-second exposure and 58% in a 20-minute exposure.

3. Denser fabrics in multiple layers

The researchers also evaluated other materials and found that tea-towel fabric, cotton-blend fabrics and antimicrobial pillowcase fabrics were your next best, and more available, option.

4. Single-layered scarves and cotton T-shirts

As the pandemic progressed, many authorities stated that any type of home-made covering can be worn over the face and nose. And while some protection is better than no protection at all, the researchers found that these options are only slightly effective – reducing your risk of infection by 44% after 30 seconds and 24% after 20 minutes.

Amanda Wilson, environmental health sciences doctoral candidate in the Department of Community, Environment and Policy in the Mel and Enid Zuckerman College of Public Health, and lead author of the study, stated that it all came down to the density and the layering of the fabrics:

"The denser the fibres of a material, the better it is at filtering. That's why higher thread counts lead to higher efficacy. There's just more to block the virus," she said. "But some masks (such as those made from silk) also have electrostatic properties, which can attract smaller particles and keep them from passing through the mask as well."

Take note of your environment

It's important to access the types of settings we enter before discarding our homemade masks and donning a mask more suited to a healthcare worker.

For example, nipping into a supermarket for 10 minutes poses a smaller risk than sitting in a crowded restaurant for hours on end.

Because no mask is 100% effective, it's vital that we reduce our risk even further by limiting our exposure to airborne droplets in poorly ventilated indoor settings. That means limiting your time in shopping malls and only running essential errands for the time being.

Wilson stated that length of exposure is a significant factor which can increase your risk – the reason for using both 20-second and 30-minute exposures in highly contaminated environments.

She also states that the size of the viral droplets from sneezing, coughing, heavy breathing or talking is very important. Larger, heavier droplets are less likely to remain airborne than smaller ones – this is why a distance of at least 2m is also recommended to help decrease your risk.

"Aerosol size can also be affected by humidity," Wilson said. "If the air is drier, aerosols become smaller faster. If humidity is higher, then aerosols will stay larger for a longer period of time, dropping out faster. That might sound good at first, but when those aerosols fall onto surfaces, the object becomes another potential exposure route," she said.

Recap on mask guidelines

Even though authorities were divided on the use of face masks, some saying early in the outbreak that they should only be worn by those who were sick, the World Health Organisation (WHO) and several other regulating bodies have since then updated their guidelines.

They advise the following:

  • Choose a mask that covers your nose and your chin – the mask should fit snugly, but comfortably to avoid pulling and tugging at your face.
  • Ensure that your mask consists of at least two layers.
  • Wash your mask after use – and ensure that you have at least two to rotate.

Wilson also says that masks should be properly fitted and pinched just above the nose, and that people shouldn't wear a mask below their noses.

"Proper use of masks is so important," Wilson said. "Also, we were focusing on masks protecting the wearer, but they're most important to protect others around you if you're infected. If you put less virus out into the air, you're creating a less contaminated environment around you. As our model shows, the amount of infectious virus you're exposed to has a big impact on your infection risk and the potential for others' masks to protect them as well," she says.

READ | Mask and Covid-19: The latest guidelines 

READ | Masks and your skin: What you should know 

READ | Importance of wearing masks during Covid-19 pandemic – amid concerns over aerosol spread

Image credit: Pille-Riin Priske from Unsplash