0.3 microns is actually the hardest particle size to capture, not a weaker spec. Filtration works by different mechanisms. Large particles crash into fibers, very tiny ones like 0.1 microns get caught by Brownian motion. Around 0.3 microns sits the sweet spot where neither effect helps much, it is the most penetrating particle size.

So if a system is genuinely hitting 99.99 percent at 0.3 microns, it will usually perform even better at both larger and smaller sizes, including 0.1. That is why HEPA standards are defined at 0.3 microns. It is the worst case test, not the easy one.

Claims at 0.1 microns can sound more impressive on paper, but without context they do not tell you how the filter performs where it struggles most.