National Academies of Sciences Engineering Medicine
"Overall, the available evidence is inconclusive about the degree to which homemade fabric masks may suppress spread of COVID-19 from the wearer to others. There are no studies of individuals wearing homemade fabric masks, in the course of their typical activities. Only limited, indirect evidence exists regarding the effectiveness of these masks for protecting others, when made and worn by the general public on a regular basis, the rapid expert consultation says."