Researchers created a test to determine which masks are the least effective

Ruben Fields
August 11, 2020

The study tested surgical masks in addition to cotton masks, neck fleece, and bandanas, which are frequently used as homemade alternatives. Each covering was tested 10 times by one speaker and three of them by four speakers.

In the test, the researchers conducted control trials on subjects without any protective face masks, speaking in the direction of a laser beam inside a dark box as a camera at the back recorded movement of droplets as they were illuminated by the laser in the box.

A person spoke towards into the hole saying the phrase "Stay healthy, people", while wearing the different types of coverings.

Perhaps unsurprisingly, the best face coverings were N95 masks (without valves), the hospital-grade type of masks used by frontline medical workers, followed by surgical masks, polypropylene masks, and cotton-polypropylene masks. Furthermore, the performance of the valved N95 mask is likely affected by the exhalation valve, which opens for strong outwards airflow.

"We confirmed that when people speak, small droplets get expelled, so disease can be spread by talking, without coughing or sneezing", Martin Fischer, Associate Research Professor in the Department of Chemistry at Duke, said in a statement.

"We could also see that some face coverings performed much better than others in blocking expelled particles". The selection of homemade cotton masks all performed within a similar range.

People receive free face masks at a Salvation Army Community Center in New York City.

Solskjaer - Germany facilities not ideal for Manchester United's Europa League prep
United hit the woodwork numerous times and had more than just one goal disallowed throughout the initial 90 minutes. "We just have to make the most out of a hard situation in conditions that are really hot, humid".

On the other hand, bandanas and neck fleeces such as balaclavas didn't block the droplets much at all. There was a big difference in material, with knitted fabric allowing more particles to pass through.

Co-author Eric Westman said he had already put the information to use, avoiding the bulk purchase of a type of mask he and a local non-profit had planned to distribute for free to the public of Durham, North Carolina where the university is based. While this does not go into the likelihood for an infected person to spread Covid-19, it's known that respiratory droplets such as these can transmit respiratory viral infections, especially in poorly ventilated areas.

Masks are important because some 30-40% of people who are infected may not show symptoms but still unwittingly spread the virus when they cough, sneeze or just talk. According to CNN, the professor wanted to make sure the masks they bought were effective.

He asked his colleagues to come up with an easy, cost-effective way to test common masks and that's exactly what Fischer did.

This extra-high number of droplets from a fleece mask is explained by the fact that the mask dispersed large droplets into a multitude of smaller droplets, leading to the researchers inferring that wearing such a mask is counterproductive in the fight against the spread of Covid-19.

Of course, the researchers are eager to emphasise that the focus of the study is actually the low-priced testing method they developed, not their own test results of which masks are the most and least effective - as the same kind of testing could be conducted more robustly and more systematically than in the proof-of-concept study here. "The notion that "anything is better than nothing" didn't hold true".

"If everyone wore a mask, we could stop up to 99% of these droplets before they reach someone else", Westman said.

Other reports by

Discuss This Article