True HEPA vs. HEPA-Type: The Clean Air Marketing Trap

### The Government Standard vs. Marketing Deception

The acronym **HEPA** stands for *High-Efficiency Particulate Air*. It was originally developed during the Manhattan Project to trap radioactive airborne isotopes.

To earn the legal designation of **True HEPA**, a filter must pass rigorous standardized testing proving that it traps at least **99.97% of airborne particles as small as 0.3 microns** (micrometers) in diameter.

Why 0.3 Microns Matters Counter-intuitively, 0.3 microns is the *most difficult particle size to capture* (the Most Penetrating Particle Size, or MPPS). Particles smaller than 0.3 microns bounce into air molecules via Brownian motion and get trapped by diffusion; particles larger than 0.3 microns get caught by impaction. If a filter can catch 0.3-micron particles at 99.97% efficiency, it catches everything larger (pollen, pet dander, dust mites) with ease.

The "HEPA-Type" Scam When you see a cheap air purifier labeled "HEPA-type", "HEPA-style", or "99% HEPA", **it is NOT a certified True HEPA filter**. These knockoffs may capture only 80% to 90% of particles, letting fine wildfire smoke and sub-micron allergens recirculate straight into your lungs. Always look for "True HEPA" on models like the **Coway Airmega AP-1512HH** or **Levoit Core 400S**.