The research into the coronavirus is running at full speed and there are some interesting new findings:
We have long suspected that the coronavirus spreads mostly via aerosols. Aerosols are not droplets. They are super fine water vapor that can stay suspended in air. Only p100 masks can filter them in significant percentages. Aerosols are normally invisible but you can see them on very cold winter days when you breath out or when you blow air form your mouth against a cold window.
This video from Dr. John Campbell called "Pandemic science, Talk quietly please" explains it really well: https://www.youtube.com/watch?v=7wJR_iwN7dc
Singing and loud speaking emits the most aerosols per second.
There is an interesting research paper about the filtration efficiency of home made cloth masks. A double layer fabric mask using different kinds of fabric for each layer can exceed the N95 specification: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7185834/. Note however that a N95 mask is far off from a P100 mask.
The trick to upgrade cloth mask to N95 level is not to use super tight fabric (that would make breathing difficult) but to combine e.g a layer of synthetic fabric with a layer of cotton fabric.
Aerosols produced during normal speech can stay for a long time suspended in the air and they can spread in the building via a HVAC system. It's however not all bad news because you can also use the HVAC system to deactivate the virus. It is possible to install a HVAC UV-light that sits in the main intake-duct. Cleaner air is better even without Covid.