What Is a ULPA Filter? How It Differs From HEPA, and Where It Actually Belongs

A ULPA filter is an Ultra-Low Penetration Air filter classified under EN 1822 Group U. The class limits are:

•U15: integral efficiency ≥ 99.9995%

•U16: integral efficiency ≥ 99.99995%

•U17: integral efficiency ≥ 99.999995%

That is the formal classification side. In the market, you will also see ULPA products described as 99.9995% at 0.1–0.2 μm or around 0.12 μm, especially in cleanroom panel products aimed at electronics. For example, a low-boron ULPA product for semiconductor use is published at 99.9995% @ 0.1–0.2 μm, and many comparison guides use 0.12 μm as the practical reference size for ULPA discussions.

When buyers ask about U15 filter efficiency, they usually want the short version:

•U15 is the entry ULPA class

•under EN 1822, it is rated at 99.9995% integral efficiency

•in product literature, it is often described around 0.1–0.2 μm performance

•it sits above H14 in filtration efficiency and usually above H14 in initial resistance and cost as well

Our engineers often see buyers mix up three different systems:

•ISO 16890 / legacy EN 779 for general ventilation filters

•EN 1822 / ISO 29463 for EPA, HEPA, and ULPA

•field terms like "medical HEPA" or "cleanroom ULPA"

Do not compare a G4, MERV 8, or ePM1 filter to a U15 panel as if they belong to the same decision tree. They do not. ULPA belongs to the absolute-filter side of the market

The basic efficiency gap is easy to state. The harder part is explaining what that gap does to the system.

Under EN 1822:

H13: ≥ 99.95%

H14: ≥ 99.995%

U15: ≥ 99.9995%

U16: ≥ 99.99995%

U17: ≥ 99.999995%

That means a ULPA vs HEPA filter decision is not just about "cleaner air." It usually affects:

Initial Pressure Drop

fan selection

FFU or terminal module energy use

replacement interval economics

leak-test and qualification expectations

whether the process truly benefits from that last fraction of efficiency

This trade-off is often clearly demonstrated in semiconductor cleanroom product lines. Their microelectronic panels are available in H14 and U15-U17 sizes, emphasizing low pressure drop, ultra-low gas release, and suitability for microelectronic cleanrooms and equipment. This powerfully illustrates that once you enter the field of semiconductor air filtration, the discussion is no longer just about removing particulate matter, but a comprehensive consideration of particle control, molecular-level cleanliness, and energy consumption.

A plain-English way to look at it

HEPA is often the right answer when the room is built around infection control, product protection, or high cleanliness without extreme particle sensitivity.

ULPA is the right answer when the process is sensitive to smaller particles, lower defect tolerance, and much tighter cleanroom targets.

That is why a blanket statement like "ULPA is better" is not useful. In many projects, ULPA is better only if the process can justify the added pressure drop and cost.

This is where application logic matters more than brochure language.

Operating rooms and healthcare spaces

ASHRAE 170 sets the filtration baseline for operating rooms at minimum MERV 16, and it specifically calls for HEPA filters at the air terminal device in certain specialty OR cases such as orthopedic procedures, transplants, neurosurgery, and dedicated burn procedures. In other words, healthcare guidance does not treat ULPA as the default answer for standard OR design. Even where HEPA is used, the goal is infection-risk control and protected airflow over the surgical field, not semiconductor-level yield protection.

So when buyers say "surgery rooms use HEPA," that is generally the right direction. The healthcare filtration target is high, but it is driven by patient safety and procedural airflow design, not by the particle and molecular sensitivity of wafer processes.

Semiconductor fabs and advanced electronics

Semiconductor facilities are a different world. Camfil's semiconductor guidance states that fabs use complete filtration and AMC-control solutions to lower particulate and molecular concentrations to ISO Class 1 levels for particles and sub-ppb levels for airborne molecular contamination. Their electronics-focused cleanroom panels are offered in HEPA H14 and ULPA U15, U16, U17, specifically for microelectronic industry and with ultra-low outgassing components.

That is why advanced chip production often moves beyond HEPA and into ULPA, especially in critical process zones, tool mini-environments, lithography areas, or other parts of the fab where smaller particles and molecular contamination directly hit yield. A practical way to say it is this:

the hospital is protecting patients and procedures

the chip fab is protecting yield at a far tighter defect threshold

Same word: clean. Very different threshold.

This is one of the details that many non-electronics buyers miss.

In semiconductor cleanrooms, the filter cannot be treated as an inert box. The filter itself can become a contamination source if the media or components outgas unwanted dopants or molecular contaminants.

A 1991 study on silicon microelectronics found that airborne boron contamination was traced to borosilicate glass in high-efficiency particulate air filters. Later industry reporting noted that traditional glass-fiber media suppliers developed low-boron products, and those media gained market acceptance in response to semiconductor requirements.

That background explains why modern electronics-grade ULPA products emphasize low-boron, dopant-free, or ultra-low outgassing construction. One current low-boron ULPA product for sub-14 nm semiconductor applications states that low-boron glass-fiber media prevents filter-borne boron contamination, and specifically warns that boron in standard ULPA media can outgas in high-purity airflow and cause unintended p-type doping. Camfil makes a similar point from another angle by promoting ultra-low outgassing, dopant-free components in its microelectronics cleanroom panels.

If your project is in:

•wafer fabrication

•lithography

•photoresist coating / exposure

•advanced packaging

•microelectronics tools or mini-environments

then the conversation should go beyond ULPA efficiency and include:

•low-boron media

•dopant-free construction

•low-organic outgassing

•compatibility with AMC-control strategy

For semiconductor air filtration, that is not a luxury item. It is part of process protection.

Our engineers usually start with the application, not the filter class.

We ask four questions first:

•What is the cleanliness target of the room or process zone?

•Is the process sensitive mainly to bioburden, particles, or molecular contamination?

•Can the system absorb the higher pressure drop that usually comes with tighter filters?

•Is the project in healthcare/pharma, or in microelectronics/semiconductor?

We recently helped a client in Southeast Asia who initially requested U15 across the entire project because their team assumed "higher grade means safer." It turned out only the critical microelectronic process areas needed ULPA. The support areas could stay on HEPA-grade terminal filtration. That change cut both fan burden and filter budget without weakening the actual process-risk controls.

That is usually the right approach. Use ULPA where it solves a real problem. Do not spread it everywhere unless the process truly needs it.

efore you finalize the specification, verify these points:

Standard: EN 1822 / ISO 29463, not general-ventilation standards

Class: H13, H14, U15, U16, or U17 based on process need

Efficiency basis: MPPS and published integral efficiency

Initial Pressure Drop: matched to the fan, FFU, or terminal module

Application: surgery / healthcare, pharma, semiconductor, or tool environment

Media risk: standard glass media, low-boron glass media, or dopant-free membrane media

Construction: low-outgassing components if used in electronics environments

Leak testing: individually scan-tested where required by the application