This is an interesting study, mostly for its insufficient conclusion.
In the experiment 4 Sars-II-patients had to cough 5 times without, with a surgical mask and a cotton mask on a petri-dish that was 20cm (sorry no freedom units here) apart from their face (please don’t tell me that there are not enough individuals involved. This is an experiment not a study. You do not need 1000 people coughing on petri dishes).
So here are the results:
“The median viral loads of nasopharyngeal and saliva samples from the 4 participants were 5.66 log copies/mL and 4.00 log copies/mL, respectively. The median viral loads after coughs without a mask, with a surgical mask, and with a cotton mask were 2.56 log copies/mL, 2.42 log copies/mL, and 1.85 log copies/mL, respectively. All swabs from the outer mask surfaces of the masks were positive for SARS–CoV-2, whereas most swabs from the inner mask surfaces were negative”
Very tiny difference right? So the conclusion should be very clear:
“In conclusion, both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment and external mask surface.”
Now, point is that the conclusion is not wrong but very insufficient. Though it is true that the virus is not filtered entirely the viral load is reduced significantly.
You might say: Wait mister! Where do you see a significant difference? From 2.56 log copies/mL to 2.42 log copies/mL that’s bullshit. I throw my face-mask into the trash right now.
The secret lies in the little word “log”, which indicates that it has to do something with logarithms. In this specific case it means that the viral load got reduced from about 388 viruses per milliliter (sorry no freedom units again) to roughly 288 viruses, a significant reduction. The reduction is much more for cotton masks. From 388 to about 71, which is a reduction of about 80 percent.
So the point is masks have a considerable effect, though it does not filter the virus entirely. Nevertheless, there is some indication that the amount of viruses that infect you might affect how sick you get and also keep in mind that it rarely happens that somebody coughs 5 times through his mask in your face like 20 non-freedom-units away from you. If he wears a cotton mask and you stand 2 meters away and maybe even hold a petri dish in front of your face, nothing might happen.
So why did this study come up with this insufficient conclusion? Because it was intended for medical staff. They need better masks. They need something that works 100 percent.