The new Duke study, published Aug. 7 in the journal Science Advances, rated a fitted N95 and a three-layer surgical mask as the top two protectors in simple tests using using a cardboard box with a lens, a laser and a phone’s camera to track particles released from a person’s mouth when speaking. Three of the next four top performers in the test included cotton.

Test subjects were asked to repeat the same phrase into the box without a mask, then repeat with each mask. Every mask was tested 10 times. (See a schematic, courtesy of Duke, of the test setup below.)

Here’s the full list, with each mask identified by a number in parenthesis corresponding to the photo above:

1. Fitted N95, no valve (14 in photo)
2. 3-layer surgical mask (1)
3. Cotton-polypropylene-cotton mask (5)
4. 2-layer polypropylene apron mask (4)
5. 2-layer cotton, pleated style mask (13)
6. 2-layer cotton, pleated style mask (7)
7. Valved N95 mask (2)
8. 2-layer cotton, Olson style mask (8)
9. 1-layer Maxima AT mask (6)
10. 1-layer cotton, pleated style mask (10)
11. 2-layer cotton, pleated style mask (9)
12. Knitted mask (3)
13. Double-layer bandana (12)
14. Gaiter-style neck fleece (11)

Here are the results, provided by Duke University:

The study’s big loser, the neck gaiter, is too thin to offer much protection, the researchers concluded.

It’s possible the fabric breaks up bigger particles into smaller particles that can remain airborne longer. Bandanas and knitted masks were similarly ineffective.

But the conclusions, as in so many other studies, have left little doubt that wearing a mask is our best defense against the spread of COVID-19.

Excerpted from "Masks Save Lives: Duke Study Confirms Which Ones Work Best." Hartford HealthCare, August 11, 2020.

Read the complete study in Science Advances