HEPA vs. ULPA Filters: Which Is Right for You?

When building or upgrading a cleanroom, one of the most critical decisions you'll face is choosing between HEPA vs. ULPA filters. Both are high-performance air filtration systems, but they serve different purposes and come with distinct trade-offs.

This guide breaks down the key differences between HEPA and ULPA filters, their applications, and how to determine which filtration system makes sense for your facility.

What Are HEPA Filters?

HEPA stands for High Efficiency Particulate Air.

According to the U.S. Department of Energy, HEPA filters must remove at least 99.97% of airborne particles that are 0.3 microns in diameter. This 0.3 micron threshold isn’t arbitrary. It represents the Most Penetrating Particle Size (MPPS), which is the hardest particle size to capture.

HEPA filters are the industry standard for cleanroom applications ranging from ISO 5 (Class 100) to ISO 8 (Class 100,000). They're used extensively in:

• Pharmaceutical manufacturing
• Medical device production
• Food and beverage processing
• Electronics assembly
• Hospital operating rooms
• Research laboratories

The majority of cleanrooms worldwide rely on HEPA filters because they strike an optimal balance between air purity, operational cost, and system efficiency.

What Are ULPA Filters?

ULPA stands for Ultra-Low Penetration Air (sometimes called Ultra-Low Particulate Air).

ULPA filters take filtration to the next level. They must remove at least 99.999% of particles 0.12 microns in diameter or larger. That's more than eight times smaller than what HEPA filters are rated to capture, and significantly more particles removed overall.

This extreme filtration capability makes ULPA filters the go-to choice for the most demanding cleanroom classifications: ISO 3 (Class 1), ISO 4 (Class 10), and sometimes ISO 5 (Class 100).

Common ULPA applications include:

• Semiconductor fabrication
• Nanotechnology research
• Advanced pharmaceutical production
• Aerospace component manufacturing
• High-precision optics production

If your process involves nanoparticles, requires single-digit particle counts, or demands the absolute highest air cleanliness, ULPA filtration is likely necessary.

HEPA vs ULPA: Key Differences Explained

Think of HEPA vs. ULPA filters like two different engine options for a vehicle. ULPA is the high-performance racing engine. It is more powerful but requires more fuel, more maintenance, and costs significantly more to operate.

Here's how they compare across critical factors:

Filtration Efficiency

HEPA: 99.97% efficient at ≥0.3 microns
ULPA: 99.999% efficient at ≥0.12 microns

ULPA filters capture smaller particles and remove a higher percentage of all particles. For context, a human hair is about 70 microns in diameter. We are talking about particles hundreds of times smaller.

Filter Media Density

ULPA filters achieve their superior performance through denser filter media. More fibers packed into the same space means more opportunities to trap particles.

This density difference is where the HEPA vs. ULPA trade-offs begin.

Airflow Capacity

Denser media creates higher resistance to airflow.

ULPA filters typically pass 20-50% less air through the same surface area compared to HEPA filters. This means you'll need more ULPA filters to achieve the same air changes per hour (ACH) in your cleanroom, which is a critical metric for maintaining proper air cleanliness.

A 2,000 square foot cleanroom that requires 20 HEPA fan filter units might need 30 or more ULPA units to maintain the same air velocity and particle removal rate.

Pressure Drop

The pressure drop across ULPA filters is significantly higher than HEPA filters.

Higher pressure drop means your HVAC system works harder. You'll need larger blowers, more powerful motors, and ultimately more electrical energy to move air through the filtration system.

This translates to higher utility bills month after month, which is a cost that compounds over the years.

Initial Cost

ULPA filters cost considerably more than HEPA filters.

Depending on size and specifications, you might pay 50-100% more per filter. When you factor in needing more total filters to achieve proper airflow, the initial investment climbs quickly.

Operating Costs

Beyond the higher purchase price, ULPA filters cost more to operate:

• Increased energy consumption due to higher pressure drop
• More air conditioning required to remove heat generated by fan motors working harder
• Greater electrical infrastructure requirements

These ongoing costs often exceed the initial filter investment over the life of the cleanroom.

Filter Lifespan

Both HEPA and ULPA filters typically last 5-10 years depending on the application and environment. These high-efficiency filters have denser media which clogs faster, even with proper pre-filtration. This means more frequent changeouts, more labor costs, and more downtime for maintenance.

How HEPA and ULPA Filters Work

Both filter types use mechanical filtration rather than electrostatic attraction. As contaminated air flows through the dense fiber matrix, particles are captured through three primary mechanisms:

Impaction: Larger particles collide directly with fibers and stick.

Interception: Medium-sized particles traveling with airflow touch a fiber and are captured.

Diffusion: The smallest particles move erratically (Brownian motion) and eventually collide with fibers.

The 0.3 micron size for HEPA filters represents the most difficult particle size to capture. It is small enough to avoid impaction but large enough to resist diffusion. ULPA filters extend this performance to even smaller particles by using finer, more densely packed fibers.

Filter Selection Based on Cleanroom Class

When considering HEPA vs. ULPA, your cleanroom classification largely determines which type of filtration is appropriate.

According to ISO 14644-1 standards, cleanrooms are classified by the maximum number of particles per cubic meter of air:

• ISO 3 (Class 1): Requires ULPA filtration
• ISO 4 (Class 10): Typically requires ULPA filtration
• ISO 5 (Class 100): Can use HEPA or ULPA depending on specific requirements
• ISO 6 (Class 1,000): HEPA filtration standard
• ISO 7 (Class 10,000): HEPA filtration standard
• ISO 8 (Class 100,000): HEPA filtration standard

The vast majority of cleanrooms operate at ISO 5 or lower classifications, making HEPA filtration the most common choice.

When to Choose HEPA Filters

HEPA filters are the right choice when:

• Your cleanroom classification is ISO 5 (Class 100) or lower
• You need to balance performance with operational efficiency
• Your process doesn't involve nanoparticles or ultra-fine contaminants
• Budget constraints make ULPA filtration cost-prohibitive
• You want longer filter life and lower maintenance frequency

For most pharmaceutical, medical device, food processing, and general manufacturing applications, HEPA filtration provides more than adequate air cleanliness while keeping operational costs reasonable.

When to Choose ULPA Filters

ULPA filters are necessary when:

• Your cleanroom must meet an ISO 4 classification or higher
• Your process involves particles smaller than 0.3 microns
• Industry regulations specifically require ULPA-level filtration
• Product contamination risk justifies the higher operational cost
• You're manufacturing semiconductors, advanced optics, or nanotechnology products

Semiconductor fabs are the most common ULPA application. Even microscopic particles can ruin a wafer worth thousands of dollars, making the investment in ULPA filtration worthwhile.

Installation Considerations

Both HEPA and ULPA filters are typically installed in:

• Fan filter units (FFUs): Self-contained units with integrated fans that mount in the cleanroom ceiling plenum
• Ducted terminal filters: Filters installed at the end of HVAC ductwork

FFUs are the most popular configuration for modular cleanrooms because they provide independent airflow control and easier maintenance access. If you're new to cleanroom design, our guide on what cleanrooms are and how they work covers the fundamentals.

When designing your cleanroom, remember that ULPA installations require:

• More ceiling coverage (more filters needed for same airflow)
• Stronger structural support (more filters = more weight)
• Higher capacity electrical service
• More robust HVAC equipment
• Increased cooling capacity

These infrastructure requirements should be factored into your initial planning and budgeting.

Pre-Filtration Matters

Regardless of your choice in HEPA vs. ULPA, proper pre-filtration extends filter life and improves overall system efficiency.

Pre-filters capture larger particles before they reach your final filters. Filtration performance at this stage is typically defined by MERV rating classifications. Common pre-filter ratings include MERV 8, MERV 11, and MERV 14.

For ULPA installations, robust pre-filtration is especially critical given the higher replacement cost and shorter lifespan of ULPA filters. Even small improvements in pre-filtration can translate to significant savings over time.

Testing and Certification

After installation, HEPA and ULPA filters must be tested to verify performance.

Common testing methods include:

• DOP testing: Measures filter penetration using dioctyl phthalate aerosol
• PAO testing: Uses polyalphaolefin particles (modern alternative to DOP)
• Particle counting: Verifies particle concentrations meet classification requirements
• Airflow uniformity: Ensures consistent velocity across the filter face

Testing should be performed after installation, after filter changeouts, and annually (or as required by your industry regulations) to maintain compliance.

The Bottom Line: HEPA vs. ULPA

For most cleanroom applications, HEPA filtration delivers the performance you need at a reasonable total cost of ownership.

ULPA filters are a specialized tool for specialized applications. They're essential for the highest cleanroom classifications but come with significant cost penalties in initial investment, energy consumption, and maintenance.

Think carefully about your actual cleanliness requirements. Many facilities overspecify their cleanroom classification, choosing more stringent standards than their process actually requires. An ISO 5 cleanroom costs substantially more to build and operate than an ISO 6. If ISO 6 meets your needs, the extra investment provides no benefit.

The right choice between HEPA vs. ULPA balances cleanliness, operational efficiency, and long-term costs.

In our experience, the most successful cleanroom projects start with a clear understanding of actual particle sensitivity rather than assumptions about what classification "should" be used.

If you're planning a cleanroom project or reconsidering your current filtration system, we're happy to talk through your specific requirements. Our team has designed filtration systems for everything from pharmaceutical manufacturing to electronics assembly, and we can help you determine whether HEPA or ULPA makes sense for your application.