The CDC conducted experiments to assess two ways of improving the fit of medical procedure masks: fitting a cloth mask over a medical procedure mask, and knotting the ear loops of a medical procedure mask, and then tucking in and flattening the extra material close to the face. Each modification substantially improved source control and reduced wearer exposure.

“Double masking” with a cloth mask over a medical mask could substantially reduce exposure to aerosols even from unmasked sources, a CDC lab study suggested. Improving the fit appears at least as important as adding fabric layers for blocking aerosol particles. Compared to an entirely maskless arrangement, fitting a dummy head with a three-ply, cotton mask over a three-ply, medical mask reduced aerosol exposure 83% when a similar dummy with no mask was the source; the reduction was nearly the same when the source dummy was double-masked and the “received” was not. These experiments highlight the importance of a good fit to maximize mask performance. There are multiple simple ways to achieve a better fit of masks to more effectively slow the spread of COVID-19. Stay the course, stay well, mask up, get vaccinated, and stay tuned!