Home-made cloth face masks likely need a minimum of two layers, and preferably three, to prevent the dispersal of viral droplets from the nose and mouth that are associated with the spread of Covid-19, say researchers.
Viral droplets are generated during coughing, sneezing, or speaking. And face masks are thought to protect healthy people from inhaling infectious droplets as well as reducing the spread from those who are already infected.
For the study, published in the journal Thorax, a team of Australian researchers compared the effectiveness of single and double-layer cloth face coverings (cotton fabric) with a 3-ply surgical face mask (Bao Thach) at reducing droplet spread.
The single-layer covering was made from a folded piece of cotton T-shirt and hair ties; the double layer covering was made using the sewing method.
The researchers used a tailored LED lighting system and a high-speed camera to film the dispersal of airborne droplets produced by a healthy person with no respiratory infection, during speaking, coughing, and sneezing while wearing each type of mask.
The study showed that the 3-ply surgical face mask was the most effective at reducing airborne droplet dispersal, although even a single layer cloth face-covering reduced the droplet spread from speaking.
But a double layer covering was better than a single layer in reducing the droplet spread from coughing and sneezing, the recording showed.
This is just one case, added to which several other factors contribute to the effectiveness of cloth face masks, the researchers noted.
These include the type of material used, design and fit, as well as the frequency of washing.
Nevertheless, based on their observations, a homemade cloth mask with at least two layers is preferable to a single layer mask, they say, adding: “Guidelines on home-made cloth masks should stipulate multiple layers.”
“There is a need for more evidence to inform safer cloth mask design, and countries should ensure adequate manufacturing or procurement of surgical masks,” the study authors noted.