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Why Is PM0.3 the Hardest Particle to Filter?

Created on 01.04

Why Is PM0.3 the Hardest Particle to Filter?

Nanofiltech Explains Air Filtration in the Simplest Way

In the air filtration industry, one statement is often repeated:
“PM0.3 is the most difficult particle size to filter.”
But why 0.3 microns?Why not 1 micron, or 0.1 micron?And why do HEPA standards always define performance at PM0.3?
As a manufacturer specializing in nanofiber filter media, HEPA/ULPA filters, HVAC filters, and industrial filter cartridges, Nanofiltech works with these questions every day.
Today, we explain—clearly and simply:
  • l Why PM0.3 is the most difficult particle size to capture
  • l Why HEPA standards are defined at 0.3 μm
  • l How nanofiber technology improves PM0.3 filtration efficiency

1. Air Filtration Is Not a “Sieve” — It Relies on Four Physical Mechanisms

Mechanical air filtration works through four combined mechanisms:

① Inertial Impaction

Large particles cannot follow airflow streamlines and collide with fibers.✔ Highly effective for particles > 1 μm

② Interception

Particles following airflow come close enough to fibers to be captured.✔ Effective for mid-sized particles

③ Diffusion

Ultra-fine particles move randomly due to Brownian motion and collide with fibers.✔ Highly effective for particles < 0.1 μm

④ Sieving

Particles larger than the pore size are directly blocked.✔ Effective for large particles
All mechanical air filters operate through these four mechanisms.

2. Why Is PM0.3 the Hardest to Filter?

Here is the key point:
Particle Size
Inertial Impaction
Interception
Diffusion
> 1 μm
Strong
Medium
Weak
< 0.1 μm
Weak
Weak
Strong
0.3 μm
Weak
Weak
Weak
PM0.3 lies exactly in the weak zone of all major capture mechanisms.
It is:
  • l Too small for strong inertial impaction
  • l Too large for effective diffusion
  • l Not close enough for strong interception
This is why PM0.3 is known as theMPPS (Most Penetrating Particle Size).
HEPA standards use 0.3 μm because:If a filter can efficiently capture PM0.3, it will perform even better at all other particle sizes.

3. Why Are Smaller Particles (0.1 μm) Easier to Filter?

This is a common misunderstanding.
From a physics perspective, ultra-fine particles are easier to capture.
Extremely small particles experience Brownian motion, moving randomly in the air.Their irregular paths increase the probability of colliding with filter fibers.
As a result:
  • l PM0.1 and PM0.05 are often captured more efficiently than PM0.3
  • l HEPA filters are highly effective at capturing virus-sized particles
  • l PM0.3 remains the most challenging size—not the smallest one

4. Why Nanofiber Technology Is Especially Effective for PM0.3

Nanofiber diameters typically range from 100–300 nm, far smaller than conventional fibers (3–10 μm).
This provides several advantages:
1. Higher fiber density and surface areaMakes particle penetration more difficult
2. More uniform pore structureReduces bypass and leakage paths
3. Surface filtration behaviorPM0.3 particles are captured at the media surface
4. High efficiency with lower pressure dropImproves energy efficiency
5. No electrostatic decayPerformance remains stable under humidity and over time
This is why industries such as semiconductors, pharmaceuticals, food processing, photovoltaics, batteries, and heavy-dust operations are rapidly upgrading to:
  • l Nanofiber HEPA / ULPA filters
  • l Nanofiber HVAC filters
  • l Nanofiber industrial filter cartridges

5. How Is PM0.3 Filtration Efficiency Evaluated?

According to international standards:
  • l H13: ≥ 99.97% @ 0.3 μm
  • l H14: ≥ 99.995% @ 0.3 μm
  • l U15: ≥ 99.9995% @ 0.3 μm
Once PM0.3 performance is achieved:
  • l Larger particles (PM1, PM2.5, PM5) are filtered more easily
  • l Smaller particles (PM0.1, PM0.05) are captured even more efficiently
  • l Virus-scale contaminants are effectively controlled
This is why Nanofiltech widely applies nanofiber and ePTFE composite technologies in HEPA/ULPA filter media.

6. Nanofiltech Solutions Optimized for PM0.3

Nanofiltech provides:
  • l Nanofiber composite HEPA / ULPA filter mediaFor semiconductors, pharmaceuticals, electronics, and laboratories
  • l Nanofiber-coated cellulose filter media for cartridgesFor metal processing, powder coating, cement, and mining
  • l ePTFE + nanofiber composite mediaFor high-temperature, high-humidity, and antistatic environments
  • l Energy-efficient HVAC high-efficiency filtersOptimized for PM0.3 capture with low pressure drop
Our advantage lies not only in high efficiency, but in stable performance throughout the entire service life.

Conclusion: PM0.3 Is Not Impossible—It Requires Advanced Technology

PM0.3 is not famous because it is the smallest particle,but because it is the most difficult to capture within filtration physics.
Nanofiber technology has fundamentally changed this challenge.
Over the next decade, driven by stricter cleanliness standards and rising energy costs, more industries will shift toward:
  • l Nanofiber HEPA filters
  • l Nanofiber HVAC filters
  • l Nanofiber industrial filter cartridges
Nanofiltech will continue advancing high-efficiency, stable, and energy-saving air filtration solutions for global industries.

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