Outward and inward protections of different mask designs for different respiratory activities

We evaluate the outward and inward protections of different mask types (N95, surgical and two cloth mask designs) taking into account the imperfect fit on the wearer. To this end, we built a manikin to simulate exhaling, coughing and inhaling of aerosol droplets 0.3–5.0 µ m in diameters. The outward and inward protections depend on many factors, including the droplet size, the mask fit and the presence of a filter layer. Here, we show that cloth and surgical masks with a non-woven filter layer can achieve a combined outward and inward protections between 50% and 90%. Removing the filter layer greatly reduces the protection efficiency to below 20% for the smallest droplet size. While a well-fitted N95 masks offer protection efficiency close to 100%, a poorly fitted N95 mask with gaps offers less protection than a well-fitted surgical/cloth mask. We also found that double masking—the wearing of cloth mask on top of a surgical mask—is only effective at reducing outward droplet emissions when coughing, while offering no additional protection when exhaling/inhaling as compared to a single cloth/surgical mask. The results of our work can inform the implementation of mask mandates to minimize airborne transmissions of coronavirus disease of 2019 (COVID-19). Practical implications 1. A single cloth/surgical mask with non-woven filter layer offers significant protection against airborne transmissions. 2. Filtering facepiece masks such as N95 respirators are unlikely to achieve the advertised high protection for the general public due to poor mask fit. 3. Double-masking offers little to no additional protection over a single cloth/surgical mask. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The authors would like to acknowledge funding from by Agency for Science, Technology and Research, Singapore (SC25/20-8R1640) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: NA All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes The data that support the findings of this study are available from the corresponding author upon reasonable request.