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Ultimate Guide to HEPA and ULPA Filters

When searching for "True" HEPA filters, H13, or IEST rated HEPA filters, not all classifications of HEPA filters are created equal. There are numerous groups and classifications that further distill HEPA performance ratings into more specific performance categories.

Terra’s HEPA and ULPA filters are specially designed for use in cleanrooms, labs, and precision assembly areas. They come in a wide range of sizes for use in Terra work stations, cleanrooms, and many other applications. They can also be used as final filtration in standalone purification systems.

Cleanroom ULPA / HEPA Filter Definitions and Requirements

Definition: Cleanroom HEPA Filters

A high-efficiency particulate air filter (HEPA), also referred to as a high-efficiency particulate absorbing filter, comprises a housing of microporous fibers that capture airborne particles and debris. HEPA filters are rated based on their particle capture efficiency for a specific particle size. By EPA standards, a HEPA filter must remove 99.97% of airborne particles 0.3 micron or larger.

Definition: Cleanroom ULPA Filters

Ultra-low penetration air (ULPA) filters capture and retain ultrafine particles sized 0.1 µm with an efficiency rate of 99.999%.

ULPA filters provide extended particle trapping efficiency beyond standard HEPA filters that capture particles up to two times smaller than the typical HEPA filter specification.

HEPA vs ULPA Filters - Advantages and Disadvantages

What are the Advantages of a HEPA Filter vs ULPA filter?

Compared to an ULPA filter, the primary advantages of a HEPA filter are cost, filter life, and energy efficiency.

For most environments, HEPA filters are able to produce logarithmic reductions in airborne pollutants and contaminants. HEPA filters are produced in a variety of styles and formats, thus making them suitable for virtually any environment without any special installation requirements. As with any filtration system purchase, it's important to keep in mind the cost and ease of filter replacement and servicing.

HEPA Filter Advantages

Microporous membranes provide excellent particle capture due to extremely small pores that diffuse and intercept particles. As a side-effect, HEPA filters require less air volume to achieve the same face velocity as an ULPA filter. As air input demands increase, HVAC systems must work harder to increase the overall air. HEPA filters are able pass through equal volumes of air at a lower fan speed, thus making them more energy efficient than ULPA alternatives. When considering the choice between HEPA or ULPA filters, one must ensure that adequate air supply is available as the backpressure increases over the life of the filter.

Meanwhile, any additional make up air requirements will incur additional heating and cooling costs.

ULPA Filter Advantages

ULPA filters are able to capture the smallest ultrafine particles more efficiently than HEPA filters. ULPA filters are essential to achieve extremely low airborne particles counts required by ISO Class 4 or ISO Class 5 (or cleaner) cleanrooms. The additional cost and shorter filter life can make them uneconomical for everyday use.

In technology, manufacturing, and research facilities ULPA filters are typically utilized where the air quality is already extraordinarily clean. ULPA filters are highly-effective when placed downstream of pre-filters or HEPA filters. ULPA filters might be specified only for areas where already clean air is recirculated and refiltered. Staged filters ensure that the largest particles are removed by larger-pore filters early in the air supply stream. Prefiltering large particles upstream of the more delicate HEPA and ULPA filters can greatly improve the filter life and reduce energy consumption caused by backpressure.

ULPA filtered laminar flow hoods, isolation rooms, or containment systems can often provide adequate and localized air quality without requiring facility-wide HVAC renovations. When used in tandem, HEPA filters can provide a more economical and energy efficient air quality approach across large floorplans.

HEPA and ULPA Filter Cleanroom Performance Standards

HEPA filters are classified according to performance standards set forth by widely recognized standards organizations such as ISO (international), EN (Europe), and IEST (US). These standards contain fundamental requirements for the testing and marking of high-efficiency particulate air filters that range in capture efficiency between 95% to 99.9995%. These performance ratings help determine what a filter can be used for, enabling clearer communication between end-users and suppliers.

EN and IEST filter testing methods are difficult to compare directly. Each test includes its own specified equipment, test medium, and measurement methods.

HEPA vs ULPA Filter Cleanroom Classifications

HEPA filters are adequate for most applications within ISO Class 5 - ISO class 8 air quality requirements. ULPA filters are specified when air quality requires ISO Class 3 - ISO Class 4 ratings.

IEST-RP-CC001 Filter Performance Ratings (Type A – K)

IEST Filter
Type PPM @		 Penetration Test Method Minimum Efficiency Rating Designated Leak Penetration
Type A
(HEPA)		 MIL-STD-282 None 99.97%, 0.3 MMD None
Type B
(HEPA)		 MIL-STD-282 None 99.97%, 0.3 MMD None
Type C
(HEPA)		 MIL-STD-282 Photometer 99.99%, 0.3 MMD 0.010%
Type D
(HEPA)		 MIL-STD-282 Photometer 99.999%, 0.3 MMD 0.0050%
Type E
(HEPA)		 MIL-STD-282 None 99.97%, 0.3 MMD None
Type F
(HEPA)		 IEST-RP-CC007 Particle counter 99.9995% at 0.1-0.2 or 0.2-0.3µm 0.00250%
Type G
(ULPA)		 IEST-RP-CC007 Particle counter 99.9999% at MPPS 0.0010%
Type H
(ULPA)		 IEST-RP-CC007 None 99.97% at 0.1-0.2 or 0.2-0.3m None
Type I
(ULPA)		 IEST-RP-CC007 None 99.97% at 0.1-0.2 or 0.2-0.3m None
Type J
(ULPA)		 IEST-RP-CC007 Particle counter or photometer 99.99% at 0.1-0.2 or 0.2-0.3m 0.010%
Type K
(ULPA)		 IEST-RP-CC007 Particle counter or photometer 99.995% at 0.1-0.2 or 0.2-0.3m 0.0080%
IEST-RP-CC001 describes 11 levels of filter performance and six grades of filter construction. The 11 category levels are described by alphabetical types ranging from Type A - Type K. Filters types H, I, J, and K are most commonly specified for high performance environments.

What is the difference between type A, B, and E HEPA filters?

  • Type A → Type B: Adds leak testing
  • Type B → Type E: same leak testing, but adds a stringent mechanical/structural construction standard (ASME AG-1) typically required for nuclear or critical safety applications

What is the difference between Type A-E HEPA filters and Type H-K HEPA filters?

The distinction between HEPA filter types (e.g., Type A–E vs. Type H–K) comes down to test standard and methodology, not performance level alone — several types across these groups share nearly identical minimum efficiency ratings. Type A–E filters are qualified per MIL-STD-282, testing at a fixed 0.3 μm particle size via photometer. Type H–K filters are qualified per IEST-RP-CC007, testing across two particle size ranges (0.1–0.2 μm or 0.2–0.3 μm, using the lower result) via particle counter.

This distinction matters because filter media has a most penetrating particle size (MPPS) — typically 0.1–0.3 μm — where efficiency is weakest. IEST-RP-CC007's range-based testing is more likely to capture this worst-case point than MIL-STD-282's single fixed size, and particle counters are more sensitive to fine-particle penetration than photometers. So while two filters with the same rating aren't necessarily different in construction or quality, a IEST-RP-CC007-based rating generally reflects a more rigorous test condition. Official type designation and performance claims should always be confirmed against the actual test method, not efficiency rating alone.

What is the most common type of IEST filter used for cleanrooms?

For standard cleanroom applications, Type C is generally the most commonly used HEPA filter designation.

  • 99.99% efficiency — this hits the sweet spot that satisfies the majority of ISO 14644 cleanroom classifications (ISO 5–8), without needing the higher cost/complexity of ULPA-grade filtration.
  • MIL-STD-282 testing — this remains the most widely referenced and recognized standard across the cleanroom, pharmaceutical, semiconductor, and industrial sectors, especially in the U.S. It's deeply embedded in legacy specs, customer requirements, and procurement language.
  • Photometer leak (scan) testing included — Type C's built-in leak test gives facilities the integrity verification needed for certification under standards like IEST-RP-CC034, ISO 14644-3, or FS 209E-derived practices, without requiring more specialized testing.

Where other types of filters fit in

  • Type A/B are less common in modern cleanrooms since they lack the photometer-based leak scan that most certification protocols require.
  • Type D (99.999%) shows up in more demanding applications — semiconductor fabs, some pharma cleanrooms — where tighter control is warranted.
  • Type H–K (CC007-based) are gaining traction as the newer IEST standard becomes more prevalent, but MIL-STD-282/Type C still dominates in practice due to how deeply it's entrenched in existing specs, customer expectations, and cross-industry familiarity.
  • ULPA (Type F/G or EN 1822 U15+) is reserved for the most stringent applications — semiconductor, aerospace, some biosafety — where ISO 3–4 classifications demand it.

EN 1822 Filter Performance Ratings (E10 – U17)

Filter Type Filter % Efficiency @ Particle Size (µm) Particle Size (µm)
E10 (EPA) 85% 150000 MPPS
E11 (EPA) 95% 50000 MPPS
E12 (EPA) 99.5% 5000 MPPS
H13 (HEPA) 99.95% 500 MPPS
H14 (HEPA) 99.995% 50 MPPS
U15 (ULPA) 99.9995% 5 MPPS
U16 (ULPA) 99.99995% 0.05 MPPS
U17 (ULPA) 99.999995% 0.005 MPPS

IEST-RP-CC001.7 vs. EN 1822 Filter Performance Testing Differences

The IEST-RP-CC001.7 and EN 1822 standards use different methods to evaluate HEPA and ULPA filter performance, making direct comparisons difficult.

What is the most common type of EN 1822 filter used for cleanrooms?

Under EN 1822, the most common HEPA filter for standard cleanroom applications is H13, followed by H14 for more demanding requirements.

Why H13 is the default:

  • 99.95% overall efficiency (at MPPS) — this satisfies most standard cleanroom classifications (comparable to ISO 6–8 range) and is the baseline most European and internationally-aligned facilities specify.
  • MPPS-based testing — EN 1822 tests each individual filter at its actual most penetrating particle size (rather than a fixed challenge size), so the 99.95% figure reflects true worst-case performance, giving strong confidence in real-world filtration.
  • Cost/performance balance — H13 is widely manufactured, broadly available, and sits at a price point that makes it the practical choice unless a project specifically calls for tighter control.

Where H14 fits in:

  • 99.995% overall efficiency — used for more critical applications: ISO 5 cleanrooms, pharmaceutical aseptic processing, semiconductor, and biosafety environments where a tighter margin is required.
  • Often the step taken instead of jumping to true ULPA (U15+) when facilities need better-than-H13 performance without the cost and complexity of ULPA-grade filtration and handling.

ULPA under EN 1822 (U15–U17) is reserved for the most stringent environments — advanced semiconductor fabrication, high-containment biosafety labs — where ISO 3–4 classification is required.

Filter Construction and Form Factor

HEPA and ULPA filters are available in a variety of dimensions and enclosure profiles. Choosing the ideal filter depends on the type of filter housing and environmental conditions.

Note: Terra’s fan filter units can use either HEPA or ULPA filter media interchangeably.

Terra filtration media consists of highly efficient microporous polyurethane mini pleats held in place by strong, rigid plastic separators that keep the medium from nesting. This design channels air flow with optimal efficiency to reduce resistance. The filter is sealed into the sturdy aluminum frame with a fire retardant adhesive. All filters are tested for air flow resistance and DOP (dioctylphthalate) smoke penetration (with a mean particle diameter of 0.3 microns) by measuring upstream and downstream concentrations.

Aluminum vs. Stainless Steel Frames

Aluminum Filter Frame Advantages / Disadvantages

Advantages: Aluminum filter frames provide a lightweight and economical alternative to steel framed filters and housings. Weight can play a factor during installation for ceiling mounted filters – lightweight aluminum filter housings are easier to lift, place, and maneuver into position. Aluminum is lighter and less costly than stainless steel, which also translates to lower shipping and handling costs.

Disadvantages: Aluminum is prone to damage and more likely to experience corrosion in the presence of cleaning agents such as chlorine and peroxides. Studies show that when aluminum is exposed to sterilization regimens such as vaporized hydrogen peroxide, ailments range between superficial oxidation and statistically significant declines in hardness.

Steel Filter Mounting Frames Advantages / Disadvantages

Cleanliness, longevity, and structural integrity make stainless steel a prototypical material choice for clean and controlled environments. Terra's all-304 stainless steel filter frames and diffusers (filter face grille) ensure optimal cleanliness and stand up to alcohol and other cleaning agents. Stainless steel fan filter components are ideal for pharmaceutical and electronics manufacturing due to its longevity, ease of cleaning, and wide resistance to chemicals, heat, and moisture.

Unlike aluminum frames, steel frames do not require a ceiling grid for installation. Steel frames enable installation within drywall or other hard ceilings that would not be feasible for aluminum frames.

Standard vs. Roomside Replaceable (RSR) Filters

Standard Fan Filter Replacement


Standard FFUs with top-side replaceable filters are an affordable option for small scale cleanrooms or enclosures. In order to change the filter, FFUs with topside replaceable filters must be entirely pulled out of the ceiling bay. Climbing up to remove the bulky FFU can be difficult, dirty, and potentially hazardous. The procedure may require tall ladders, multiple people, personal protective equipment, and shutting down the cleanroom.

Roomside Replaceable Fan Filter Replacement (RSR Filters)


RSR filters provide a detachable filter assembly that is swappable without removing the entire fan filter unit from the cleanroom ceiling or hood. These filters are ideal for environments where filters require frequent testing, servicing, and replacement.

Instead of using screws or other fasteners, a roomside replaceable filter is clamped in place with special clips and covered by a snap-in diffuser screen. A gel-filled channel seats securely against a "knife-edge" on the blower housing to form an air-tight seal.

Polyurethane Fan Filter Sealants

For semiconductor production, filters require a fire-retardant, phosphorus-free, polyurethane sealant to prevent the contamination of sensitive electronics, components, chips, and packages.

Cleanroom particulate is the typical suspect for product contamination; however, molecular contamination must also be considered. For example, Fyrol PCF can cause phosphorus contamination when used in HEPA filter gasket materials. As air passes through a filter, the adsorption and desorption of ionic micro contaminants into the airstream can cause unintended reactions with wafer surfaces. Components exposed to organophosphates may experience adhesion problems and variations in oxide growth, thus leading to less reliable performance, shorter working life, and potential device failure.

For the manufacturing of electronics, circuit boards, and wafers, select filter units sealed with a fire retardant, phosphorus free polyurethane sealant.

Terra's Whisperflow Fan Filter Units are equipped with FDA-approved acrylic urethane sealant to minimize leaks and off-gassing.

Cleanroom Pre-Filter: Selection Guide

What is a Cleanroom Pre-Filter? Do I Need One?

Cleanroom pre-filters capture larger particles and contaminants before they reach the downstream HEPA filter. Pre-filters are available in numerous formats and specifications.

All Terra fan filter units include an integrated MERV 7 pre-filter.

How Do Cleanroom Pre Filters Improve HEPA Performance and Longevity?

Prefilters not only reduce the cost and frequency of replacing filters, but also provide energy savings and lower the risk of premature wear on the fan motors. When a cleanroom operation is running tens or hundreds of fan/filter units, these savings can add up quickly.

The operational life of filter media is largely determined by the cleanliness of the operations, air flow rate, efficiency, and particle composition. Depending on the facility, HEPA filter replacement intervals vary between 6 months to 10 years. To maximize this working life, prefilters reduce HEPA filter work loads by intercepting larger particles upstream.

Surprisingly, HEPA filters become more efficient at trapping particles over the life of the filter. That's because as more particles become trapped in the filter, filtration efficiency increases as a result of particles having fewer paths to escape from the increasingly dense media fibers. As the filter becomes more saturated, particle entrapment becomes more efficient.

The downside is that a late-life HEPA filter will require significantly more supply air to achieve the same output (CFM) as a newer filter. The blower will have to run at higher speeds to compensate, increasing energy costs and wear-and-tear on the motor.

These classes refer to environments with reduced particulate contamination, not to creating sterile environments. Consult your industry standards for sterile environments. Terra Universal's BioSafe stainless steel cleanrooms may be ideal for sterile applications since they are not affected by harsh wash-down chemicals.

What is the Right Pre Filter for My Facility / Application?

For a pre-filter to a downstream HEPA or ULPA filter, Terra recommends a MERV 7 filter. This filter grade greatly increases the longevity of your higher-efficiency filters without significantly restricting the air supply to the blower.

Pre-filtration can also be used in the building HVAC to extend the life of HEPA/ULPA filters. Some common recommendations include MERV 13 for office buildings, MERV 14 for medical facilities and MERV 8 for outside air intakes in urban areas.

MERV Filter Selection by Building Type

MERV Rating Filter will Trap Particles sizes 0.3 to 1.0 microns Filter will Trap Particles sizes 1.0 to 3.0 microns Filter will Trap Particles sizes 3 to 10 microns Removes These Particles
MERV 1-4 < 20% < 20% < 20% Pollen, Dust Mites, Spray Paint, Carpet Fibres
MERV 5 < 20% < 20% 20% - 34% Pollen, Dust Mites, Spray Paint, Carpet Fibres
MERV 6 < 20% < 20% 35% - 49%
MERV 7 < 20% < 20% 50% - 69%
MERV 8 < 20% < 20% 70% - 85%
MERV 9 < 20% < 50% ≥ 85% Mold Spores, Cooking Dusts, Hair Spray, Furniture Polish
MERV 10 < 20% 50% - 64% ≥ 85%
MERV 11 < 20% 65% - 79% ≥ 85%
MERV 12 < 20% 80% - 90% ≥ 90%
MERV 13 < 75% ≥ 90% ≥ 90% Bacteria, Smoke, Sneezes
MERV 14 75% - 84% ≥ 90% ≥ 90%
MERV 15 85% - 94% ≥ 95% ≥ 90%
MERV 16 ≥ 95% ≥ 95% ≥ 90%

What is the most Common MERV filter used for cleanrooms?

For most cleanroom fan filter units, Terra recommends a MERV 7 pre-filter. A MERV 7 pre-filter effectively captures larger airborne particles while maintaining low airflow resistance, helping extend HEPA or ULPA filter life, reduce energy consumption, and minimize fan motor wear. Higher-MERV pre-filters generally provide little additional benefit in FFU applications because the downstream HEPA or ULPA filter performs the critical fine-particle filtration.

Need Help Selecting Filters for Your Cleanroom or Filtration Device?

Contact a Terra Cleanroom Specialist for assistance across many applications including positive pressure, negative pressure, and hazardous environments.

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