#Duke University face mask researchers share more details on study results

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The 14 face masks studied by Duke University researchers — unranked.
Emma Fischer, Duke University

We all need to wear masks in public spaces to prevent the spread of COVID-19 — but not all of them are created equal.

And little was known about how effective each one was at stopping respiratory droplets.

That is, until Duke University researcher Dr. Martin Fischer came up with a simple test to measure it.

The experiment, published Friday in the journal Science Advances, tested 14 different types of masks and was inspired by a request from Fischer’s co-worker Dr. Eric Westman, who works with Cover Durham, an initiative to distribute reusable face coverings to those in need. Westman asked if someone at the school could assure him that the masks he received as donations were effective.

To test the coverings, scientists outfitted a black box with a laser and a cellphone camera and had four testers try out the 14 donated options. Wearing each mask, A tester would speak in the direction of the laser beam inside the box, saying the phrase “Stay healthy, people” five times. A camera recorded the amount of respiratory droplets set off by the speech, and an algorithm determined how many droplets had leaked through the face covering.

“The was about setting up a simple measurement technique that can be reproduced,” Fischer told The Post.

And while he doesn’t advocate for any specific mask, Fischer — who wears a basic cotton version himself — says the overarching point of the study is that many of the varieties are pretty effective. But you’re better off wearing a real mask than something that makes you look like a bandit trying to stick up a bank in the Wild West.

Here’s a breakdown of face coverings Fischer and his team put through the paces, from the strong sealed medical N95 mask to the flimsy neck gaiter.

The best

1. medical n95 mask

No wonder the fitted “3M 1860 Surgical Mask and Particulate Respirator” is worn by health-care workers: It was the most effective of the bunch on the study’s logarithmic scale.

2. surgical mask

This disposable surgical mask was the second most effective variety, ranging from zero to 0.1 in terms of the particles spread from speaking while wearing one.

3. polypropylene and cotton

The synthetic material polypropylene, laid in between two layers of cotton, was the third best.

4. polypropylene apron mask

This mask made with two layers of the synthetic material was just marginally worse than the one made with both cotton and polypropylene.

5. cotton mask with ties

The next six cotton masks all performed around the same level, which Fischer said shows variables matter. “It depends how loud you speak, and how well it fits around your face,” or if facial hair causes a looser fit, he said.

6. two-layer cotton with ties

Right behind the green tie mask was another cotton version with two layers, and straps that went across the bottom and tied behind the ears.

7. valved n95

N95 masks with exhalation valves are designed to protect the user from breathing in harmful materials not necessarily the other way around, which could have contributed to its performance.

8. hand-sewn cotton

This cotton mask was sewn using the popular “Olson” pattern, which is available online.

9. ‘MAXIMA AT’ mask

A pleated cotton variety from North Carolina-based company Hudson’s Hill was essentially tied with the similar-looking single-layer cotton mask to the left.

10. single-layer cotton

This one-layer mask performed better than one with two layers, which should serve as a reminder of the variables in the experiment and in life, said Fisher.

11. pleated two-layer cotton

This two layered cotton pleated style mask, performed just slightly worse than its other similar styles.

12. knitted

A mask made from what appears to be a tee-shirt knit (Fisher was keen to point out the researchers are not textile experts) had more of variability of droplet projection than other styles.

13. bandana

Adored by celebrities such as Johnny Depp and Kristen Stewart, the folded bandana has become a chic covering option, but it’s basically useless, multiple studies — including Duke’s — have found.

The worst

14. neck gaiter

The stretchy gaiter tested here (a style beloved by runners) was worse than forgoing a mask completely, and was shown to break the larger particles into smaller ones, allowing them to slip out of the sides more easily.