To her, some of the most compelling evidence in favor of face masks comes from laboratory tests. A Florida team used mannequin heads to simulate coughing and sneezing and lasers to illuminate the tiny respiratory droplets believed to the main route of transmission. Without masks, the droplets traveled more than 8 feet. A stitched, double-layer cotton mask limited the spread to 2.5 inches...Another lab study...Yet another team used a bird flu virus as a stand in for the novel coronavirus and showed that even homemade paper and cloth masks could block penetration of more than 95 percent of virus-laden aerosols.