Which mask works best? To visualise droplets and aerosols, UNSW researchers used LED lighting system & a high-speed camera, filming people coughing and sneezing in different scenarios — using no mask, two different types of cloth masks, and a surgical mask.
We confirmed that even speaking generates substantial droplets. Coughing and sneezing (in that order) generate even more. A three-ply surgical mask was significantly better than a one-layered cloth mask at reducing droplet emissions caused by speaking, coughing and sneezing, followed by a double-layer cloth face covering. A single-layer cloth face covering also reduced the droplet spread caused by speaking, coughing and sneezing but was not as good as a two-layered cloth mask or surgical mask.
We do not know how this translates to infection risk, which will depend on how many asymptomatic or mildly symptomatic infected people are around. However, it shows a single layer is not as good a barrier as a double layer.