Bandannas, gaiters and knitted masks are some of the least effective face coverings for preventing the spread of coronavirus, according to a new study.
Researchers at Duke University made the discovery while testing 14 different types of masks, according to the study published Friday.
N95 masks, often used by health-care professionals, worked best to stop the transmission of respiratory droplets during regular speech.
Other good performers at stopping leakage were three-layer surgical masks and cotton masks, which can be made at home, the researchers with Duke's physics department found.
But while bandannas and knitted face coverings may be a unique look, they did not offer much protection, according to the study.
The scientists also discovered that neck fleeces, or neck gaiters, often worn by runners, were the least effective and actually allowed more respiratory droplets to escape than not wearing a mask at all.
That's because they were shown to break down larger droplets into smaller particles, allowing them to slip out the sides of the covering more easily.
"We were extremely surprised to find that the number of particles measured with the fleece actually exceeded the number of particles measured without wearing any 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 made use of a black box outfitted 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 were recorded by the camera in the back of the box.
A computer algorithm then counted the droplets seen in the video to determine how many had leaked through.
The researchers said this was a low-cost, effective method to test which face coverings worked and which didn't.
"This is a very powerful visual tool to raise awareness that a very simple masks, like these homemade cotton masks, do really well to stop the majority of these respiratory droplets," Fischer told CNN.
"Companies and manufacturers can set this up and test their mask designs before producing them, which would also be very useful."This report originally appeared on NYPost.com.