The efficacy of fabric masks is once again up for debate thanks to a recent article on RNZ. Naomii Seah digs deeper.

We’ve all heard the advice on masks: wear one. Make sure it goes over your nose and mouth. Make sure it fits snugly. Sounds simple, right? 

But masking has become a particularly contentious issue, with anti-maskers making it hard for those with legitimate mask exemptions to access essential services. 

Recently, a New Zealand study found that washing and reusing “single-use” medical masks still provided relatively high filtration and protection from Covid-19-size particles. An RNZ story on the research claimed the study found medical masks washed 10 times were still “more effective” than “triple-layer fabric masks”. The story received more than 1,200 reactions on Facebook, and, as of November 25, had been shared 354 times.

Many were left with the impression that cloth masks “don’t work”. 

But researchers Richard Everts, a Nelson-based infectious diseases specialist, and Lucy Telfar-Barnard, from the University of Otago’s department of public health, who both worked on the study, say they “definitely firmly disagree” that cloth masks are useless. In fact, Telfar-Barnard herself has penned an excellent (and research-based) article for us on how to ensure your home-made mask is effective.

The main focus of Everts and Telfar-Barnard’s study – which seems to have got a bit lost in all the hubbub about cloth masks – is that yes, you can wash and re-wear a “single-use” medical mask. 

Everts, who led the study, points out that this is particularly important research for developing countries. When the pandemic began, he was in Vanuatu, and witnessed the country’s realisation that they had no masks – not even for healthcare workers. An order was placed with the World Health Organisation, but Everts knew “they simply didn’t have the resources” to treat those supplies as single-use. 

When he came home, Everts began thinking about our own communities. He realised that for a range of reasons, many New Zealanders wouldn’t – or couldn’t – discard medical masks after a single use. 

“You’ll probably find that a lot of people are already washing [single-use] masks,” says Everts. “This study was designed to guide those people.”

And they’ve proved that washing a “single-use” mask has limited effects on the fabric filtration properties. “If people want to reuse a mask,” says Everts, “then by washing it in warm water and drying it overnight, that’s going to have little effect on the fabric itself.” 

But there’s a lot more to the efficacy of a mask than just its material. 

“In public comment I’m always very careful to emphasise that fit is of paramount importance,” says Telfar-Barnard. “If you can’t find a way to make a surgical mask fit, then a cloth mask may be a better option.” 

Everts agreed, adding “there’s huge gaps around your nose, by your cheeks, and under your chin, depending on your face shape and how you’re wearing [the mask]. And those gaps are going to let through 40, 60, 70% of all the air. So the mask is only as good as it fits. That hasn’t been part of this study.” 

Everts’s claim is backed up by current research, such as this 2021 UK study that concludes that the filtration of fabrics doesn’t matter as much as having a mask that properly fits. They found that all types of currently available masks will release “secondary jets” of completely unfiltered air. Of course, glasses wearers are already aware of this issue.

So the recent media framing of Everts and co’s research – that all medical masks are better than all cloth masks at protecting against infection – is simply untrue.  

A brief skim of the team’s research methods shows they didn’t test fabric masks at all. Instead, they tested strips of “a cotton T-shirt, a 400-thread-count 100% cotton pillowcase, and a 250-thread-count cotton-polyester mix pillowcase”. For one of the trials, they stacked each cloth sample in threes. 

“I didn’t choose [those fabrics] for any particular reason,” says Everts. “I suppose I was thinking of a developing country. What fabrics are available over there, or to someone who lives rurally.” 

But again, they didn’t test homemade masks, or any of the many cheap and available commercial non-medical fabric masks. They also didn’t combine fabrics, as many at-home mask makers do. 

They did test disposable medical masks, but only three types. Everts acknowledges there are hundreds of brands of medical masks, and their efficacy will also vary. With any mask, Everts says, “there’s going to be a range, from really good ones to the cheaper ones that let more virus particles through”. 

But before we freak out about “efficacy”, it’s important to point out that lab-testing conditions for masks are fundamentally different to conditions of everyday mask use. Everts stresses that their experiment only focuses on the filtration of the fabrics. It doesn’t necessarily tell us about the real transmission risks for users.

Everts tells me their study was aligned with international testing regulations for mask production. It’s essential to note that guidelines around mask development are explicitly aimed at medical contexts. For Everts’s study, the process of fabric testing involved spraying saline at a teacup-saucer-size area of the fabrics. But this isn’t how any of us are exposed to Covid-19. 

Quite apart from that, the central purpose of wearing masks is to prevent infection from spreading to others, and even a single-layer cotton mask will catch 99.9% of large droplets from the wearer.

The central issue for community members looking to protect themselves, says Telfar-Barnard, is that “what [cloth masks] do is far more variable [compared to medical masks]”. A user of a medical mask needs to ensure fit, but choosing or making a fabric mask involves consideration of fit, fabric, layers and nose wires.

But masks work. Yes, even fabric masks. One as yet unreviewed study from the University of Cambridge, released this January, did test commercially available fabric masks. The researchers considered transmission risk as a whole, accounting for fit and filtration, and they used a human model as opposed to a saline jet. They found that simple, two-layer cotton masks blocked 62.6% of airborne particles, and more sophisticated fabric masks with panels and a filter blocked 87.1% of airborne particles. In the same study, a survey was conducted that found the public generally underestimated the efficacy of fabric masks. 

“I would rather people wore something that fits them, is comfortable, and they comply [with Covid-19 regulations] than not wear a mask at all,” says Everts. His advice for vulnerable community members – the immunocompromised, the elderly, those with chronic conditions – is that “the better the mask [you] wear, and the better it fits, the more it will benefit [you]”. 

But for the general public, who are well and follow existing Covid-19 guidelines? 

It’s “no big deal” what mask you wear, Everts laughs.