Respiratory protective equipment (RPE) is widely used to limit the transmission of viruses and bacteria, representing a critical means of controlling Covid-19. In particular, respirator masks of the FFP3/N95 types, originally designed to protect against airborne dust particles, have been widely used to protect healthcare workers (Fig 1). It is essential that these masks fit tightly against the face to make an airtight seal, checked by fit testing. However, these masks are typically designed for a white male workforce, providing a limited range of size and geometry. This can lead to overtightening to compensate for a poor fit, which is associated with soft tissue injuries, as well as an increased risk of infection. This multidisciplinary project will investigate the fit and biomechanics of RPE devices, to ensure provision of a safe interface with users. Computational modelling and MRI will be used to explore how the soft tissues of the face deform in contact with a mask. These models will be informed through experimental monitoring of mechanical and thermal loads during RPE application and the associated changes in local skin physiology. In addition, the project will utilise existing databases of face shapes to investigate the fit of masks on a more representative range of users. This will lead to the development of design templates for new masks (working with UK manufacturers), standard test methods (STMs) to evaluate the risk of facial injury (working with testing and standards organisations), and intelligent fitting software to ensure that users select the correct mask.