Evidence shows that cloth masks, particularly those with several layers of cotton cloth, block droplet and aerosol contamination of the environment, which may reduce transmission of COVID-19.
The point is not that some particles can penetrate the mask, but that some particles are stopped, particularly outwardly, from the wearer, said first author Catherine Clase, associate professor of medicine at McMaster University and a nephrologist of St. Josephs Healthcare Hamilton…..
https://brighterworld.mcmaster.ca/articles/evidence-shows-cloth-masks-may-help-against-covid-19/