HEPA and ULPA filters are among the most cutting-edge filtration systems, capable of capturing particles invisible to the naked eye. While they share the same function, they differ in nearly every other aspect.
This guide will break down everything you need to know about HEPA and ULPA filters in cleanrooms. By the time you’re finished reading, you’ll have enough knowledge needed to make an informed decision about which filters to install in your cleanroom.
What Is A Hepa Filter?
HEPA (High-Efficiency Particulate Air) filters are specialized mechanical air filters that capture at least 99.97% of particles as small as 0.3 microns.
They function using a dense web of glass or synthetic fibers arranged in pleats, trapping contaminants like dust, pollen, and bacteria through three primary mechanisms:
Inertial impaction: Larger particles collide with the fibers and become trapped.
Interception: Mid-sized particles adhere to the fibers as they follow the airflow.
Diffusion: Ultrafine particles move erratically due to air molecule interactions, increasing the likelihood of being captured.
These filters meet strict U.S. Department of Energy standards and are essential in hospitals, labs, and manufacturing facilities where air purity matters.
Cleanroom HEPA Filters
In cleanrooms, HEPA filters maintain ISO-classified air quality by removing contaminants from the supply air. Modern systems often use fan filter units (FFUs) instead of traditional ducted setups, as they are more cost-effective to install and easier to maintain.
FFUs limit face velocity to 0.5 m/s to prevent particles from blowing past the filter. They’re also sealed with airtight gel gaskets to prevent leaks that could compromise sterile environments.
HEPA filters in cleanrooms make it possible to manufacture semiconductors and pharmaceuticals, where even microscopic contaminants can ruin products.
HEPA Filter Efficiency
HEPA filter efficiency depends on particle size and design. While they’re tested to capture 99.97% of 0.3-micron particles (the hardest size to trap), their performance improves for both larger and smaller particles. For example:
- Pollen (10+ microns): >99.99% capture rate
- Bacteria (1–5 microns): 99.995% efficiency
- Viruses (~0.1 microns): Up to 99.999% due to diffusion effects
Independent lab tests show HEPA filters reduce aerosolized viruses like influenza by 99.99% in controlled environments.
HEPA Filter Specification
Standard cleanroom HEPA filters follow precise engineering guidelines:
- Grades: H13 (99.99% efficiency) for most ISO 5–7 cleanrooms
- Dimensions: Common sizes include 610×610 mm and 1220×1220 mm
- Airflow: 450–900 m³/hour per filter module
- Certification: Passes MIL-STD-282 aerosol leak tests
Operating limits range from 4.4°C to 37.8°C (39.9°F to 100.0°F) and 25%–75% humidity. Exceeding these conditions can lead to filter warping or mold growth.
What Is A ULPA Filter?
ULPA (Ultra-Low Penetration Air) filters are advanced air filtration systems capable of removing at least 99.999% of particles as small as 0.12 microns, including dust, viruses, and bacteria.
These filters consist of densely packed synthetic or glass fibers arranged in pleated layers, capturing contaminants through three primary mechanisms:
- Inertial impaction: Traps larger particles
- Interception: Captures mid-sized particles
- Diffusion: Prevents the passage of sub-0.1-micron particles
Unlike HEPA filters, which target 0.3-micron particles, ULPA filters target even smaller contaminants, making them essential for semiconductor fabrication and pharmaceutical sterile processing.
Cleanroom ULPA Filters
In ISO Class 1–3 cleanrooms, ULPA filters maintain ultra-low particle counts by filtering supply air through ceiling-mounted fan filter units (FFUs) or ducted systems. Key applications include:
- Semiconductor manufacturing: Reduces defects by 40% compared to HEPA filters
- Pharmaceutical aseptic processing: Ensures sterility in drug production
- Nanotechnology labs: Prevents interference from submicron particles
Modern ULPA systems prioritize low face velocity (<0.45 m/s) to prevent particle bypass and, just like HEPA, use gel-sealed housings for airtight installation.
ULPA Filter Efficiency
Efficiency depends on particle size and test standards:
| Particle Size | Efficiency | Testing Standard |
| ≥0.12 microns | 99.9995% | EN 1822, ISO 29463 |
| 0.1–0.2 microns | 99.999% | IEST-RP-CC007 |
Independent studies show ULPA filters achieve:
- 99.9998% capture of 0.12-micron particles under MIL-STD-282 testing
- 99.9995% efficiency against oil smoke and chemical aerosols
ULPA Filter Specification
Standard specifications include:
- Grades: U15 (99.9995%), U16 (99.99995%), U17 (99.999995%) per EN 1822
- Dimensions: 610×610 mm to 1220×1220 mm
- Airflow: 250–750 m³/h per module
- Materials: Fire-retardant fiberglass with MERV 20-rated media
- Certifications: Passes PAO aerosol leak tests and IEST-RP-CC034 protocols
Operating limits: 4°C–38°C temperature range, 20–80% humidity. Filters exceeding these parameters risk reduced efficiency or structural damage.
HEPA Vs ULPA – Advantages & Disadvantages
HEPA Filters
HEPA filters represent an optimal balance between filtration efficiency and operational costs.
Their 99.97% efficiency at 0.3 microns proves sufficient for most medical and industrial applications, while their larger pore size allows for higher airflow rates and lower energy consumption.
This translates to operating costs approximately 25-30% lower than comparable ULPA systems.
Maintenance requirements for HEPA systems remain relatively straightforward. These filters typically maintain effective filtration for 3-5 years under normal operating conditions, with straightforward validation using DOP (DiOctyl Phthalate) testing.
The initial installation costs remain moderate, and the filters demonstrate remarkable resilience across a broader range of humidity conditions (25-75% RH).
HEPA filters have become the preferred choice for general cleanroom applications, hospitals, and pharmaceutical manufacturing facilities where ISO Class 5-8 cleanliness suffices.
Their cost-effectiveness and reliable performance make them the industry standard for most critical air filtration needs.
ULPA Filters
ULPA filters, with their superior filtration capability of 99.999% at 0.12 microns, serve as the gold standard for ultra-precise environments like semiconductor manufacturing.
This enhanced performance, however, comes with significant operational considerations. The denser filter media requires stronger fan systems to maintain adequate airflow, resulting in energy consumption typically 40-50% higher than HEPA systems.
Additionally, ULPA filters generally need replacement 1.5 times more frequently than HEPA filters due to the faster loading of their finer filter media.
These systems demand more rigorous maintenance protocols, requiring quarterly PAO (Poly-Alpha Olefin) testing and typically lasting 2-3 years before replacement. The more stringent testing requirements can increase annual maintenance costs by 60-75% compared to HEPA installations.
Initial installation costs for ULPA systems average 45-60% higher than comparable HEPA systems due to more sophisticated mounting requirements and the need for more precise airflow control systems.
The specialized nature of ULPA filter manufacturing also results in unit costs typically double those of equivalent HEPA filters.
ULPA filters show optimal performance within a narrower band of environmental conditions (20-60% RH), and temperature fluctuations above 38°C can compromise the integrity of their filter media more readily than HEPA materials.
Despite these constraints, ULPA systems remain essential for specialized applications requiring ISO Class 1-4 environments. These include:
- Advanced semiconductor fabrication
- Nanotechnology research
- Critical aerospace component manufacturing
These types of industries are where the additional costs are justified by the required ultra-pure environment.
HEPA Vs ULPA – Key Differences
A comprehensive understanding of the differences between HEPA and ULPA filters requires examining several key technical aspects that set these filtration technologies apart.
Let’s explore these differences systematically to understand why each type serves specific purposes in different applications.
1. Filtration Efficiency
The most fundamental difference lies in their filtration efficiency standards. While HEPA filters must capture 99.97% of particles at 0.3 microns, ULPA filters achieve a remarkably higher standard of 99.999% efficiency at an even smaller particle size of 0.12 microns.
To put this in perspective, if we had 100,000 particles of 0.3-micron size, a HEPA filter would allow 30 particles to pass through, while a ULPA filter would allow only 1 particle of 0.12-micron size to pass through.
This difference might seem small, but it proves its worth in environments where even minimal contamination could cause significant problems.
2. Physician Construction
The physical construction of these filters reveals another important distinction. HEPA filters typically employ a less dense arrangement of glass or synthetic fibers, with pore sizes averaging around 0.3 microns.
ULPA filters, in contrast, use a much denser configuration of fibers, creating smaller pore sizes averaging 0.12 microns.
This structural difference directly impacts airflow characteristics – HEPA filters allow for higher air velocities of up to 0.5 m/s, while ULPA filters must operate at lower velocities, typically below 0.45 m/s, to maintain their exceptional filtration efficiency.
3. Testing Methodology
Testing methodologies also differ significantly between these two filter types. HEPA filters undergo DOP (DiOctyl Phthalate) testing, which uses particles specifically sized at 0.3 microns to verify their performance.
ULPA filters require more sophisticated PAO (Poly-Alpha Olefin) testing, which can detect much smaller particles and ensure the higher level of filtration efficiency these filters must maintain.
This difference in testing reflects the more stringent quality control requirements for ULPA filters.
4. The Classification System
The classification systems for these filters also highlight their distinct capabilities. HEPA filters are typically classified as H13 (99.95%) through H14 (99.995%), according to EN 1822 standards.
ULPA filters extend this classification system further, ranging from U15 (99.9995%) through U17 (99.999995%). This progression in classification demonstrates the increasingly stringent requirements for particle capture as we move from HEPA to ULPA technology.
5. Manufacturing Processes
Manufacturing processes for these filters also exhibit notable differences. HEPA filters can be produced using relatively straightforward pleating and assembly techniques, while ULPA filters require more precise manufacturing controls and specialized materials.
The fiber diameter in ULPA filters is typically 20-30% smaller than in HEPA filters, and the pleating density is significantly higher to achieve the required filtration efficiency.
This manufacturing precision contributes to the substantial cost difference between the two filter types.
6. Application Environments
Application environments for these filters differ based on their capabilities. HEPA filters find widespread use in medical facilities, pharmaceutical manufacturing, and general cleanroom applications where ISO Class 5-8 cleanliness levels are sufficient.
ULPA filters become necessary in more demanding environments like semiconductor fabrication, nanotechnology research, and aerospace component manufacturing, where even the slightest contamination could have severe consequences.
These applications require ISO Class 1-4 cleanliness levels that only ULPA filters can consistently maintain.
7. The Monitoring and Maintenance Requirements
The monitoring and maintenance requirements for these systems reflect their different levels of sophistication.
HEPA systems typically require annual or semi-annual testing and certification, while ULPA systems demand quarterly testing and more frequent filter replacements.
This difference in maintenance schedules stems from both the higher sensitivity of ULPA filters to contamination and the more critical nature of the environments they protect.
HEPA Vs ULPA – Choosing the Right Filter for Your Cleanroom
Here’s what your thought process should look like when deciding between HEPA or ULPA filters for your cleanroom:
1. Understand Your Cleanroom Requirements
Selecting the appropriate filtration system begins with a thorough assessment of your cleanroom’s specific needs. The most critical factor is determining the required ISO classification for your facility.
This classification directly correlates with the maximum allowable particle concentrations in your cleanroom environment.
For instance, if your cleanroom needs to maintain ISO Class 5 or higher (less stringent), a HEPA filter system will typically suffice. However, for ISO Classes 1-4, where particle counts must remain extremely low, ULPA filtration becomes necessary.
2. Evaluating Process Sensitivity
The sensitivity of your manufacturing or research processes plays an important role in filter selection. Consider how particle contamination might affect your end product or research outcomes.
In semiconductor manufacturing, where circuit patterns can be smaller than 0.1 microns, even minimal contamination can render products unusable, making ULPA filtration essential.
Conversely, in pharmaceutical compounding or medical device assembly, where the critical particle size is typically larger, HEPA filtration often provides adequate protection while offering better cost efficiency.
3. Assessing Operating Costs and Budget Constraints
Understanding the long-term financial implications of your filtration choice is essential for sustainable cleanroom operation.
HEPA systems generally require 25-30% less energy than ULPA systems due to their lower pressure drop requirements.
Additionally, maintenance costs differ significantly – HEPA filters typically need replacement every 3-5 years, while ULPA filters may require replacement every 2-3 years.
Factor in, not just the initial installation costs, but also the ongoing operational expenses, including energy consumption, maintenance requirements, and replacement schedules.
4. Considering Environmental Factors
Your facility’s environmental conditions significantly impact filter performance and longevity. HEPA filters maintain their efficiency across a broader range of humidity levels (25-75% RH) and temperature conditions.
If your facility experiences fluctuating environmental conditions or cannot maintain strict climate control, HEPA filters might be the more reliable choice.
ULPA filters require more stable conditions (20-60% RH) and more precise temperature control to maintain their ultra-high efficiency levels.
5. Analyzing Space and Infrastructure Requirements
The physical constraints of your facility deserve careful consideration. ULPA systems often require more sophisticated mounting systems and additional ceiling height to accommodate their larger housings and more complex air handling requirements.
Your existing HVAC infrastructure might need significant modifications to support ULPA filtration, whereas HEPA systems typically integrate more easily with standard cleanroom designs.
Consider whether your facility can accommodate these structural requirements without major renovations.
6. Future-Proofing Your Investment
Think about your facility’s future needs when selecting a filtration system. If you anticipate upgrading to more sensitive processes or stricter cleanliness requirements, investing in ULPA filtration initially might prove more cost-effective than upgrading from HEPA later.
However, if your current and projected future needs align well with HEPA capabilities, choosing ULPA filtration might represent unnecessary overcapacity and expense.
Final Words
Ultimately, choosing between HEPA and ULPA filtration requires balancing technical requirements, operational constraints, and cost considerations.
If HEPA filtration meets your cleanliness standards, it is often the more practical choice due to its lower operating costs and easier maintenance.
Opt for ULPA filtration when ultra-pure environments are essential or when working with highly sensitive materials, where the higher costs are justified by the critical nature of your operations.