- A face-mask experiment from researchers in Australia found that homemade masks should have at least two layers, and ideally three, to be effective at preventing coronavirus spread.
- The researchers spoke, coughed, and sneezed while wearing a single-layer mask made from a t-shirt, and double layer hand-sewn mask, no mask, and a surgical mask.
- The WHO also suggests people wear homemade masks with at least three layers.
After testing the efficacy of different homemade face masks to trap droplets being sprayed from a person's mouth, researchers found that face coverings need at least two layers to be effective.
For the study, the researchers at the University of New South Wales in Sydney, Australia, spoke, coughed, and sneezed, while wearing a single-layer mask made of a T-shirt, and then a double-layer mask that was sewn using the CDC-suggested method.
They also did the experiment with no mask at all, and a surgical mask.
Using a video camera and LED lights, the researchers could see the amount of droplets that were able to get through the masks they tested.
They found that the single-layer homemade mask reduced the spread of droplets during speaking, and said this confirmed that, "even a single-layer face covering is better than no face covering."
But the double-layer mask was better than a single-layer for reducing droplets while speaking, and proved "significantly better" than the single-layer for catching droplets from coughing and sneezing.
The researchers said the surgical mask was the best form of coverage in all three scenarios, but but these masks are not recommended for the general public, as a way to protect the supply for healthcare workers.
WHO recommends masks with at least 3 layers
Since the coronavirus pandemic ramped up in the United States, mask-wearing and the best types of masks have become a point of contention among the public, and public-health experts and officials.
In early April, Insider reporters Hilary Brueck and Gabby Landsverk wrote that the CDC and WHO organization cautioned the public against wearing
But both organizations have since changed their stances, and the WHO specified that three-layer masks are the best homemade option for reducing coronavirus spread.
According to epidemiologist Maria D. Van Kerkhove, the WHO technical lead on
Masks aren't perfect, but they can help
The WHO's director-general Tedros Adhanom Ghebreyesus has warned people about being over-reliant on face coverings.
"I cannot say this clearly enough: Masks alone will not protect you from COVID-19. Masks are not a replacement for physical distancing, hand hygiene, and other
Ben Cowling, a professor of epidemiology and a mask researcher at the University of Hong Kong's School of Public
"The argument ... about everybody wearing a mask is not that it will prevent everyone from getting infected — it's that it will slow down transmission in the community a bit," Cowling previously told Insider. "That's already useful. Just to have even a small effect is useful."
The researchers of the homemade-mask experiment said that layers aren't the only important factor in DIY-mask efficacy, but their demonstration proves it does matter to an extent.
They said the type of material used, how each layer is arranged in the mask, and how often the mask is washed could also play a role in overall effectiveness. For the time being, they suggested people aim to wear three-layer homemade masks for optimal protection.
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