Using lasers, a cell phone camera and a simple computer algorithm, Duke researchers have published a method for testing the adequacy of certain types of masks in reducing respiratory droplets.
https://advances.sciencemag.org/content/early/2020/08/07/sciadv.abd3083
This test was designed to be cheaply and easily reproducible by mask makers and other entities who would be interested in knowing mask effectiveness.
Duke researchers tested common masks available to the public.
Non-valved N95, as expected, provided the best filtering of droplets. Three layer surgical masks also performed very well. Cotton cloth masks did fairly well.
N95 masks with valves leak a lot of droplets from the wearer. They would protect the wearer from droplets but will expose those around them to the droplets from the wearer.
Bandanas didn't work very well.
Fleece masks actually made droplets worse.
https://advances.sciencemag.org/content/early/2020/08/07/sciadv.abd3083
This test was designed to be cheaply and easily reproducible by mask makers and other entities who would be interested in knowing mask effectiveness.
Duke researchers tested common masks available to the public.
Non-valved N95, as expected, provided the best filtering of droplets. Three layer surgical masks also performed very well. Cotton cloth masks did fairly well.
N95 masks with valves leak a lot of droplets from the wearer. They would protect the wearer from droplets but will expose those around them to the droplets from the wearer.
Bandanas didn't work very well.
Fleece masks actually made droplets worse.