In their blog, Public use of masks to control the coronavirus pandemic
researchers at the University of Bath hypothesize
that public uses of masks may help control the coronavirus pandemic. The idea is that masks help reduce the spread of the virus by reducing the amount of droplets expelled and inhaled. The blog notes that surgical and N95 masks appear to be effective. Non-medical masks appear to be effective as well according to the blog. The research found that the effectiveness of improvised masks are unknown because of flawed study controls.
In another older study, A cluster randomised trial of cloth masks compared with medical masks in healthcare workers
found that infection rates for healthcare workers using cloth masks were higher, than the infection rates for worker using medical masks. The study concluded that cloth masks are not suitable for healthcare workers.