A properly designed scientific study has been done of different types of face masks, rating their effectiveness against spreading the water droplets that carry Corona virus and which spread Covid-19 disease:
Inexpensive, Accessible Device Provides Visual Proof that Masks Block Droplets | Duke Health
The experiments were performed with a laser based system that can visualize and display the water droplets exhaled as someone speaks in a normal voice. The link includes a video showing this.
The history of masks in medical usage was primarily to protect the physicians and nurses from catching infections from patients. That’s the main reason they have been wearing them since the bird beak masks in the middle ages.
This study shows that some of the most effective masks (like certain N95 masks) are not effective against the community spread of virus because of the construction of the valve in them. Some N95 masks have a one way valve that only prevents inhaling particles, not exhaling particles.
Also the one layer polyester “gaiters” that you wear on your neck and pull up over your face are NOT effective against spreading virus.
Thankfully this study did identify masks – many of which are inexpensive multi-layer cloth masks – that are effective. The video is worth watching.
The study is at:
Low-cost measurement of facemask efficacy for filtering expelled droplets during speech | Science Advances
with the PDF at: