Yo sk1986,
We exhale/sneeze/coughs as aerosols and the water in these aerosols evaporate and becomes this thing called droplet nuclei. The dessicated droplet nuclei consists of proteins and stuff in addition to viruses and range around 1 micron, dropping down to around 0.3 microns min. This is regardless of SARS-Cov-2, measles virus, cold viruses all the common ones like rhinovirus, 229E all are agglomerated together.
There is no such thing as 1 single virion floating in the air, this is a very common misconception.
All the
Made in Korea KF94s can block. Note, MIK KF94, coz there are some 3D masks that are not KF94s and have less filtration, there are some 3D masks that claim BFE 99.9% but not KF94 that measure a wee bit less on the meter (eg on a hazy day the meter measures say 13-26 for the KF94 and for the BFE 99.9% mask measures around 50, while those made in china KF94 measures in the 300-600 particles / L range, and some 3D anti droplet masks measure 5000-9000 particles/L)
I have not met/measured a single MIK KF94 that measures bad or "fail" from qoo10, regardless of price, after measuring about a dozen brands. (not that i have that many, is coz other pax sent me samples to measure)
Note, the most important part is that you guard against leakages at tne nose bridge and upper cheeks. Followed by leaks at the chin area. In higher risk scenarios, you can use some 3M micropore tape (1/2 inch size is enough) to tape up at the edges so that there is no leak.
And seriously, you only get sick after a certain viral load exposure (they call this the viral innoculum), you dont get sick with just a few viral particles inhaled. Unless you immunity cui.
So, really depends.
Just for more eg and reference, this fella measures at 0.064 microns, with the mask fitted on his face.
Here's another source on a PFE machine, testing on the filter performance solely.
He uses 0.1 micron particles.