What Is HEPA? A Widely Misused Catch-All Term

In the market, pleated filters are commonly lumped together under the name HEPA. That is simply a catch-all term people adopted for convenience when referring to this class of product — strictly speaking, it is not accurate.

What Actually Qualifies as HEPA

HEPA stands for High Efficiency Particulate Air.

It generally refers to filter media with an extremely high filtration efficiency on a specific particle size, typically requiring an efficiency of 99.95% or 99.97% and above. However, the specific definition and test conditions differ from one standard to another.

How Different Standards Define It

IEST-RP-CC001.7 (US standard)

· Type A: tested with PAO as the challenge aerosol, requiring filtration efficiency of 99.97% and above on particles of 0.3 micron and larger.

· Type H: the challenge aerosol may be PAO, DOP, or other media, requiring filtration efficiency of 99.97% and above on particles of 0.1–0.2 or 0.2–0.3 micron.

EN 1822 (European standard)

The challenge aerosol for EN 1822 testing may be DEHS, PAO, PSL, and is not limited to these substances. It requires testing the filtration efficiency at MPPS (the Most Penetrating Particle Size) at ≥99.95%, and the test may be run with or without discharging the electrostatic charge.

Why the EN1822 Doesn't Apply to Air Purifier Filters

Filter pads used in air purifiers are typically made from electret meltblown filter paper. Once the electrostatic charge is discharged, this class of media has an extremely low filtration efficiency, and its MPPS efficiency falls below the paper's nominal grade. EN 1822 therefore does not apply to HEPA filters used in air purifiers, and its grades cannot be used to endorse this type of filter.

Diagram comparing particle capture in electret filter media with the electrostatic charge present versus discharged

About Us

Dongguan Walson Environmental Purifying Technology Co., Ltd. (Walson) is an air purifier filter factory located in Dongguan, Guangdong.

Diagram of the factory testing capability and scale: wind tunnel laboratory, 81 m³ test chamber, chemical analysis laboratory, plus plant size, headcount, monthly capacity and certifications

Our customers today are mainly air purifier brand owners and manufacturers, as well as aftermarket and after-sales dealers.