Decent mask study (This is peer reviewed/published)
A cotton mask led to an approximately 20% to 40% reduction in virus uptake compared to no mask
In contrast, when a mask was attached to the mannequin that released virus, cotton and surgical masks blocked more than 50% of the virus transmission, whereas the N95 mask showed considerable protective efficacy (Fig. 2C). There was a synergistic effect when both the virus receiver and virus spreader wore masks (cotton masks or surgical masks) to prevent the transmission of infective droplets/aerosols (Fig. 2D and E).
https://msphere.asm.org/content/5/5/e00637-20#F2