1. They didn't test the material using actual virus particles. They used salt.
The aerosol particles are generated using a commercial sodium chloride (NaCl) aerosol generator (TSI Particle Generator, model #8026), producing particles in the range of a few tens of nanometers to approximately 10 μm.
Salt atoms are naturally ionized. I doubt covid-19 particles have the same level of ionization, but this isn't addressed in the study.
2. They don't tell you the humidity level, that I could find, during the test. Everyone knows very low humidity helps with electrostatic charge. Ever been shocked during a kiss after walking across the carpet on a low humidity day? It doesn't happen when the humidity is high.
3. Since your hot humid breath is passing through the fabric, the fabric masks are going to quickly lose a lot of their electrostatic capture ability. If it's hot and you sweat, the mask is actually going to get wet.
4. They tried to simulate leakage. They estimated a 0.5%~2% leakage around the mask which they simulated by drilling holes. That's laughable for anything less than a N95 mask. By now, we have all worn a cloth mask and know the leakage is significant. The hot moist air leaking out is what fogs your glasses. Many people wear their masks loosely to improve breath-ability. Don't get me started on the bandanas tied around the face or the cloth masks with an exhaust valve. They are laughable.
5. They only tested at low CFM's to simulate regular breathing and breathing during exercise. Regular breathing expels air at about 7 mph. Coughs can hit 50 mph and sneezes can hit 100 mph.
6. The materials they checked all had a breath-ability difficulty level of a N95 mask or higher! Experts steer people to fabric masks because they are easier to breath through, but that isn't true is you layer the materials and/or use really tight weaves. They found quilt material with a batting almost a 1/4 inch thick was very effective. Would you like to try and breath through that all day?
Here is a chart showing the pressure differentials they tested equaled or were much higher than N95 masks.
7. The study only addresses particle size filtration by various mask materials. It doesn't address the fact that people touch their faces much more when wearing a mask and don't change or wash the mask as often ans recommended.
8. This was a laboratory study, not a real world study. Do masks reduce covid-19 spread in the real world? There are lot's of models that predict they "may" reduce the spread, but if you aren't skeptical of models at this point, I can't help you. Remember when models claimed 2.5 million Americans were going to die from covid-19? Models also claimed the Arctic would be ice free now. It's not.
Here is an article about a study of the reduction of covid-19 infection in public from mandatory masks. They found a whopping 2% reduction. (Bold is by me.)
Many people feel mandatory mask wearing is a violation of their rights. Masks are certainly burdensome on the public. A 2% reduction is almost statistically insignificant. Let the people who want to wear masks wear them and let the rest of us make our own health choices.Researchers said wearing face masks in public reduced the daily number of coronavirus by as much as 2% in Washington, D.C. and the 15 states that mandated face mask use compared to states that did not.