Face coverings and respiratory tract droplet dispersion:
https://royalsocietypublishing.org/doi/abs/10.1098/rsos.201663
To summarize:
They measured how well a mask could block the movement of water droplets - coming from the mouth of a person speaking or coughing, or artificially released through the head of a mannikin. In all cases, both surgical and cloth masks effectively blocked the particles, such that 10,000 fewer particles were measured at a distance of 6 feet when masks were used.
This suggests that masks are, in fact, effective in blocking large particles that contain virus. However, the researchers say that their research can't really be used to conclude that masks are effective if smaller aerosolized particles are important in disease transmission (as now seems to be the case).