how big is a particle of COVID virus and what size particles does my flimsy little blue mask stop?
Virtually none to none. The devil is in the details- they just hide the details.
in raw numbers a CV pathogen is around .125 micron and various masks ( using the N95 as a baseline- cloth masks are 100% useless) are about .1 to .3- so the professionals say it will stop about 95% particles ( those sizes are averages within a range- never absolute values)
The first lie is filtering- let me explain. Filter media efficiency standard is a metered number of particles at a given size in an ISO rig at a set air velocity for ONE time pass then count the particles. That's where that 95% efficiency comes from.
What they failed to say was that media was stretched to a specific tension for air permeability on the test rig and only blown through ONCE. ( one pass filtration) When you breathe in and out that velocity exceeds the test and now you are MULTIPLE PASS filtration thus negating the test relative to the application.
The second lie is consistency over time- your "mask" is flexing and all that. That changes the micron rating ( always larger) but thats not part of the test standard so they just don't mention that part. The more you breathe,wear,move,adjust- the more open it becomes.
The third lie is retention- you have only 1 membrane layer (imagine a woven rope chain link fence) the acceleration causes the particles to change velocity and get stuck BUT as you wet it ( moisture) and move- you are constantly shaking those fibers and media passes right on through. ( not part of a single pass test so they don't mention that either)
These are all industry standard ISO testing requirements for all filter media ( google and read up)
They know this and are deliberately misrepresenting the data.
There's much more.