Face coverings and respiratory tract droplet dispersion Supplementary Information. # Background: # Respiratory droplets are the primary transmission route for SARS-CoV-2; a principle which drives social distancing guidelines. Evidence suggests that virus transmission can be reduced by face coverings, but robust evidence for how mask usage might affect safe distancing parameters is lacking. Accordingly, we set out to quantify the effects of face coverings on respiratory tract droplet deposition. # Methods: # We tested an anatomically-realistic manikin head which ejected fluorescent droplets of water, and human volunteers, in speaking and coughing conditions without a face covering, with a surgical mask and/or a single layer cotton face covering. We quantified the number of droplets in flight using laser sheet illumination and UV-light for those that had landed at table height, from 0·25 m up to 2 m. For human volunteers, expiratory droplets were caught on a microscope slide 5 cm from the mouth. # Findings: # Whether manikin or human, wearing a face covering decreased the number of projected droplets by > 1000-fold. The effect was so marked that wearing a face mask rendered droplets virtually undetectable at any tested distance. We also estimated that a person standing 2 m from someone coughing without a mask is exposed to over 10,000 times more respiratory droplets than someone standing 0.5 m from someone wearing a basic single layer mask. # Interpretation: # Our results indicate that face coverings show consistent efficacy at blocking respiratory droplets and thus provide an opportunity to moderate social distancing policies. However, the methodologies we employed mostly detect larger (non-aerosol) sized droplets. Whilst SARS-CoV-2 is spread by respiratory droplets and the fomites they generate, the relative importance between these modes of transmission and true aerosol transmission is uncertain. If aerosol transmission is later determined to be a significant driver of infection, then our findings may overestimate the effectiveness of face coverings.Accordingly, we set out to quantify the effects of face coverings on respiratory tract droplet deposition. # Structure: # The information is grouped into four, zipped, datasets: Dataset 1: UV light test - droplets deposition images https://doi.org/10.7488/ds/2897; Dataset 2: Microscopy tests - droplets deposition images https://doi.org/10.7488/ds/2899; Dataset 3: Laser tests - droplets path images https://doi.org/10.7488/ds/2900; Dataset 4: Shadow Imaging https://doi.org/10.7488/ds/2909. For processing the larger image files, users may need to use the Python code for use with Jupyter Notebook, in the two .ipynb files. All the datasets are part of the Collection "Face coverings and respiratory tract droplet dispersion" https://datashare.is.ed.ac.uk/handle/10283/3729 .The information is grouped into four, zipped, datasets: Dataset 1: UV light test - droplets deposition images https://doi.org/10.7488/ds/2897; Dataset 2: Microscopy tests - droplets deposition images https://doi.org/10.7488/ds/2899; Dataset 3: Laser tests - droplets path images https://doi.org/10.7488/ds/2900; Dataset 4: Shadow Imaging https://doi.org/10.7488/ds/2909. For further details, please download the ReadMe.txt file from each dataset. For processing the larger image files, users may need to use the Python code for use with Jupyter Notebook, in the two .ipynb files.