With everyone wearing different styles of facemasks, Duke University physician and professor Eric Westman wondered: Are each mask-sellers' claims of efficacy true? Which masks are the most effective, and which simply provide a false sense of security?
As reported by Duke Health, Westman's colleague Martin Fischer, the chemist and physicist in charge of Duke's Advanced Light Imaging and Spectroscopy facility, devised a scientific test using a laser. Subjects spoke through a variety of masks, and the airborne droplets that made it through the mask were counted.
Types of Masks Tested (Not Ranked, Just Numbered)
1. 'Surgical' (Surgical mask, 3-layer)
2. 'Valved N95' (N95 mask with exhalation valve)
3. 'Knitted' (Knitted mask)
4. 'PolyProp' (2-layer polypropylene apron mask)
5. 'Poly/Cotton' (Cotton-polypropylene-cotton mask)
6. 'MaxAT' (1-layer Maxima AT mask)
7. 'Cotton 2' (2-layer cotton, pleated style mask)
8. 'Cotton 4' (2-layer cotton, Olson style mask)
9. 'Cotton 3' (2-layer cotton, pleated style mask)
10. 'Cotton 1' (1-layer cotton, pleated style mask)
11. 'Fleece' (Gaiter type neck fleece)
12. 'Bandana' (Double-layer bandana)
13. 'Cotton 5' (2-layer cotton, pleated style mask)
14. 'Fitted N95' (N95 mask, no exhalation valve, fitted)
'Swath' (Swath of mask material, polypropylene)
'None' (Control experiment, no mask)
Test Results
The most surprising result is that wearing the fleece mask was worse than wearing no mask at all. As Fischer explains, the fleece essentially serves as an aerator on a sink faucet--it not only lets the droplets through, but breaks them up into finer droplets, allowing them to remain in the air longer.
Finally, for clarity's sake, we've arranged the images of the masks in order of efficacy.
Mask Types Ranked in Order of Efficacy:
Ranked #1
14. 'Fitted N95' (N95 mask, no exhalation valve, fitted)
Ranked #2
1. 'Surgical' (Surgical mask, 3-layer)
Ranked #3
5. 'Poly/Cotton' (Cotton-polypropylene-cotton mask)
Ranked #4
4. 'PolyProp' (2-layer polypropylene apron mask)
Ranked #5
(Not pictured) 'Swath' (Swath of mask material, polypropylene)
Ranked #6
13. 'Cotton 5' (2-layer cotton, pleated style mask)
Ranked #7
7. 'Cotton 2' (2-layer cotton, pleated style mask)
Ranked #8
2. 'Valved N95' (N95 mask with exhalation valve)
Ranked #9
8. 'Cotton 4' (2-layer cotton, Olson style mask)
Ranked #10
6. 'MaxAT' (1-layer Maxima AT mask)
Ranked #11
10. 'Cotton 1' (1-layer cotton, pleated style mask)
Ranked #12
9. 'Cotton 3' (2-layer cotton, pleated style mask)
Ranked #13
3. 'Knitted' (Knitted mask)
Ranked #14
12. 'Bandana' (Double-layer bandana)
Ranked #15
'None' (Control experiment, no mask)
Ranked #16
11. 'Fleece' (Gaiter type neck fleece)
So yeah, if you see someone in the store wearing a fleece mask, probably better to steer clear.
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