N95 masks, often used by healthcare professionals, worked best to stop the transmission of respiratory droplets during regular speech.
The three-layered surgical masks and cotton masks, which can be made at home, also found researchers in Duke’s physics department have found other good agents to stop the leaks.
But while knitted bandanas and headwear may be a unique look, they don’t offer much protection, according to the study.
Scientists also found that neck fleeces, or neck warmers, often worn by runners, were the least effective and actually allowed more respiratory droplets to escape than not wearing a mask at all.
This is because they have been shown to break down larger droplets into smaller particles, allowing them to slide more easily down the sides of the coating.
“We were extremely surprised to find that the number of particles measured with the fleece actually exceeded the number of particles measured without wearing a mask,” Martin Fischer, one of the study’s authors, told CNN.
“We want to emphasize that we really encourage people to wear masks, but we want them to wear masks that actually work.”
To test the masks, the scientists used a black box equipped with a laser and a cell phone camera.
Someone wearing a face mask would speak in the direction of the laser beam inside the box. Then, the amount of respiratory droplets scattered by the beam was recorded by the camera on the back of the box.
A computer algorithm then counted the droplets seen in the video to determine how many had filtered.
The researchers said it was an efficient and inexpensive method of testing which face coatings worked and which did not.
“It’s a very powerful visual tool to educate the public that a very simple mask, like these homemade cotton masks, does very well at stopping the majority of these respiratory droplets,” Fischer told CNN.
“Companies and manufacturers can set this up and test their mask designs before they produce them, which would also be very helpful.”