The protection provided by face coverings varies greatly: 10-90% more protective than wearing nothing, depending on the size of the particles the person is exposed to and the fit of the covering.

Studies have shown that surgical face masks are effective at reducing the emission of virus particles when talking, sneezing, and shouting. (Full article: Exhaled respiratory particles during singing and talking (tandfonline.com))

Face shields, however, only seem to reduce large droplet emissions at the range 0.1-0.5m and have a minimal effect on reducing the number of smaller particles emitted. 

Studies also suggest that face coverings designed for respiratory protection (FFP2/N95) would likely be more protective than surgical masks and cloth face coverings, provided they fit the face snugly, forming a seal around the nose and mouth. (Modeling the filtration efficiency of a woven fabric: The role of multiple lengthscales: Physics of Fluids: Vol 34, No 3 (scitation.org))

Related