KN95 masks are rated to capture 95% of tiny particles (0.3 micron particles, to be exact). People will often assume that masks can’t capture particles smaller than 0.3 microns.
If that was true, then it wouldn’t make sense that masks do a really good job of preventing virus transmission. Luckily, that's not true.
Contrary to popular opinion, particles smaller than 0.3 microns are actually easier to capture. You can learn more about the science behind it here.
KN95 Masks are even tested for fit. This ensures that the leakage of outside air into the covered area around your mouth and nose while the mask is being used is kept to a minimum.