What Is a HEPA Filter?
A HEPA (High-Efficiency Particulate Air) filter captures at least 99.97% of airborne particles at 0.3 microns — the most penetrating particle size. True HEPA is graded H13–H14 (and higher ULPA grades exist). It is used where very clean air is essential: hospitals, cleanrooms, labs, and high-end air purifiers.
How HEPA filters work
HEPA media is a dense mat of fine fibres that captures particles through interception, impaction, and diffusion. Counterintuitively, 0.3 microns is the hardest size to catch — both larger and smaller particles are captured even more efficiently, which is why the 99.97% rating is specified at that size.
HEPA grades
| Grade | Efficiency | Use |
|---|---|---|
| H13 | 99.95% | Cleanrooms, hospitals, purifiers |
| H14 | 99.995% | Critical / pharmaceutical |
| U15–U17 (ULPA) | 99.9995%+ | Semiconductor, nanotech |
Frequently Asked Questions
What does HEPA stand for?
HEPA stands for High-Efficiency Particulate Air. A true HEPA filter captures at least 99.97% of particles at 0.3 microns.
Is HEPA better than MERV 13?
HEPA captures far more fine particles than MERV 13, but it requires specialized housings and stronger fans. For standard HVAC, MERV 13 is the practical choice; HEPA is for critical environments and dedicated purifiers.
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