“Fit is vitally important—loose masks leave plenty of room for pathogens to travel—and N95s and KN95s, with their tighter fit, are clearly the mask of choice to maximize protection in all situations and on all forms of transportation. Dr. Wafaa El-Sadr, professor of epidemiology and medicine at Columbia University Mailman School of Public Health, acknowledges that comfort counts too and worries about people starting a flight (or other long trip on public transport) with a highly protective mask and then shucking it midway, since N95 masks are more restrictive than most cloth or surgical masks.”