Duke University researcher Martin Fischer, who put the test together, told CNN: "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. The league table of the 14 masks tested (picture number): 1. N95 mask, no exhalation valve, fitted (14) 2. Surgical mask (1) 3. Cotton-polypropylene-cotton mask (5) 4. Two-layer polypropylene apron mask (4) 5. Two-layer cotton, pleated style mask (13) 6. Two-layer cotton, pleated style mask (7) 7. N95 mask with exhalation valve (2) 8. Two-layer cotton, Olston style mask (8) 9. One-layer Maxima AT mask (6) 10. One-layer cotton, pleated style mask (10) 11. Two-layer cotton, pleated style mask (9) 12. Knitted mask (3) 13. Bandana (12) 14. Gaiter type neck fleece (11)