Types of Cleanroom Filters: Pre-Filters, Mid-Range, HEPA, ULPA

In modern high-tech industries, cleanrooms are essential for product quality and production environment stability. To maintain the cleanliness levels of a cleanroom, selecting the right air filters is crucial. This article will introduce four types of specialized cleanroom air filters and provide relevant technical data.

What Are Cleanroom Filters?

Cleanrooms are controlled environments designed to minimize contamination from airborne particles, microorganisms, and other pollutants. To achieve and maintain the required level of cleanliness, high-performance air filters play a critical role in removing impurities from the air.

Cleanroom filters are specifically engineered to prevent particles, bacteria, and viruses from entering the controlled space. The selection of the right filter is essential, especially in high-sensitivity industries such as semiconductors, pharmaceuticals, and healthcare, where maintaining air purity directly impacts product quality and production stability.

Types of Cleanroom Filters

The primary types of cleanroom air filters include pre-filters, medium efficiency filters, HEPA filters, and ULPA filters. The following is a detailed introduction to each type:

• Pre-Filters

  
  
  
  Pre-filters serve as the first line of defense in a cleanroom air filtration system. Their primary function is to capture larger airborne particles (3-10µm), such as pollen, dust, skin flakes, and mold spores. By removing these larger contaminants early in the process, pre-filters help extend the lifespan of HEPA and ULPA filters while maintaining overall efficiency.
  
  Since pre-filters are exposed to higher levels of contaminants, their replacement frequency depends on environmental conditions. In most cleanroom applications, it is recommended to replace pre-filters every 2 to 6 months to ensure optimal performance.
  
  ACDT’s pre-filter is designed for durability and efficiency. Its moisture-proof cardboard frame prevents deformation, while the V-pleated media maximizes filtration area for superior performance. Plus, the tightly sealed filter media prevents air leakage, providing cleaner air and a longer lifespan.
  
  
  

• Medium Efficiency Filters

  
  
  
  Medium efficiency filters are designed to capture airborne particles ranging from 1 to 3µm, providing a filtration efficiency of 60% to 95% depending on the specific filter rating. These filters act as a middle layer between pre-filters and high-efficiency filters, effectively trapping medium-sized particles.
  
  By removing these contaminants before they reach HEPA or ULPA filters, medium efficiency filters play a crucial role in extending the lifespan of higher-grade filtration systems while maintaining stable airflow.
  
  ACDT’s medium efficiency filters offer a high-performance solution with minimal frame usage and a large filtration area. Built with galvanized steel and specially reinforced for durability, these filters resist deformation and ensure long-term stability. Available in efficiency levels of 60-65%, 80-85%, and 90-95%, they cater to various air quality needs. Designed to meet ASHRAE standards, these synthetic pocket filters provide superior airflow and reliability.
  
  
  

• HEPA Filters (High-Efficiency Particulate Air Filters)

  
  
  
  HEPA filters are designed for high-precision air filtration, effectively capturing 99.97% of airborne particles as small as 0.3µm. These filters meet stringent U.S. Department of Energy (DOE) and European EN 1822 standards, making them essential for environments that demand exceptional air purity.
  
  Due to their superior filtration efficiency, HEPA filters are widely used in semiconductor manufacturing, pharmaceutical facilities, and medical environments, where even the smallest contaminants can compromise product integrity or patient safety. To ensure consistent performance, HEPA filters should be replaced every 4 to 6 years, depending on industry requirements and maintenance schedules.
  
  ACDT’s HEPA filters deliver exceptional air purification, achieving 99.99% to 99.995% filtration efficiency at 0.3µm. Designed with a mini-pleat structure, these filters maximize surface area while reducing airflow resistance, ensuring stable and efficient performance. Built to meet EN1822 Class H13/H14 standards, they are ideal for cleanrooms, semiconductor manufacturing, pharmaceuticals, and biotech laboratories.
  
  
  
  

• ULPA Filters (Ultra-Low Penetration Air Filters)

  
  
  
  ULPA filters provide an even higher level of air filtration than HEPA filters, capable of capturing 99.9995% to 99.99995% of airborne particles as small as 0.1-0.12µm. This exceptional filtration efficiency makes ULPA filters essential for ultra-clean environments where even microscopic contaminants can cause significant issues.
  
  These filters are particularly suited for medical cleanrooms, semiconductor fabrication, and advanced electronics manufacturing, where maintaining extreme air purity is critical. By preventing ultra-fine pollutants from compromising highly sensitive products, ULPA filters ensure a stable and contamination-free production environment.
  
  ACDT’s ULPA filters are designed for ultra-high efficiency, capturing 99.9995% to 99.99995% of particles as small as 0.12µm. Utilizing advanced mini-pleat technology, they maximize filtration surface area while maintaining low pressure drop, ensuring stable airflow and energy efficiency.

Filter Efficiency Standards Comparison Tables

• EN 779:2012 Classification Table

  
  The EN 779:2012 standard classifies air filters based on the following criteria:
  
  

  Filter Class	Final P.D (Pa)	Average Arrestance (Am) (%)	Average Efficiency of 0.4 µm particles (Em) (%)
  G1	250	50 ≤ Am < 65	–
  G2	250	65 ≤ Am < 80	–
  G3	250	80 ≤ Am < 90	–
  G4	250	90 ≤ Am	–
  M5	450	–	40 ≤ Em < 60
  M6	450	–	60 ≤ Em < 80
  F7	450	–	80 ≤ Em < 90
  F8	450	–	90 ≤ Em < 95
  F9	450	–	95 ≤ Em

  
  Notes:
  • Grades G1 to G4 are classified based on Average Arrestance (Am).
  • Grades M5 to F9 are classified based on Average Efficiency of 0.4µm Particles (Em).
  • Under standard testing conditions, the maximum final pressure drop for coarse filters (G1-G4) is 250 Pa, while the maximum final pressure drop for fine filters (M5-F9) is 450 Pa.
    
    
    

• Combined ISO 29463-1:2024 and EN 1822-1:2019 Filter Classification Table

  
  

  ISO 29463-1:2024						EN 1822-1:2019
  Filter class	GROUP	Overall value		Local value a,b
  		Efficiency (%)	Penetration (%)	Efficiency (%)	Penetration (%)
  ISO 05 E	E	≥ 85	≤ 15	—	—	E10
  ISO 10 E		≥ 90	< 10	—	—	—
  ISO 15 E		≥ 95	≤ 5	—	—	E11
  ISO 20 E		≥ 99	≤ 1	—	—	—
  ISO 25 E		≥ 99.5	≤ 0.5	—	—	E12
  ISO 30 E		≥ 99.90	≤ 0.1	—	—	—
  ISO 35 H	H	≥ 99.95	≤ 0.05	≥ 99.75	≤ 0.25	H13
  ISO 40 H		≥ 99.99	≤ 0.01	≥ 99.95	≤ 0.05	—
  ISO 45 H		≥ 99.995	≤ 0.005	≥ 99.975	≤ 0.025	H14
  ISO 50 U	U	≥ 99.999	≤ 0.001	≥ 99.995	≤ 0.005	—
  ISO 55 U		≥ 99.9995	≤ 0.0005	≥ 99.9975	≤ 0.0025	U15
  ISO 60 U		≥ 99.9999	≤ 0.0001	≥ 99.9995	≤ 0.0005	—
  ISO 65 U		≥ 99.99995	≤ 0.00005	≥ 99.99975	≤ 0.00025	U16
  ISO 70 U		≥ 99.99999	≤ 0.00001	≥ 99.9999	≤ 0.0001	—
  ISO 75 U		≥ 99.999995	≤ 0.000005	≥ 99.9999	≤ 0.0001	U17

  
  Notes:
  • According to EN 1822-1:2019, Group E filters cannot be leak-tested for classification.
  • According to ISO 29463-1:2024, the local penetration values for Group H filters are for reference only for the MPPS particle scanning test method. Different standards can be set for photometer or oil leak tests.
    
    

Data Source:

• • INTERNATIONAL STANDARD ISO-29463-1-2024
  • INTERNATIONAL STANDARD EN 1822-1:2019

Conclusion

Selecting the right air filter is crucial for maintaining cleanroom cleanliness. It is recommended to choose cleanroom filters based on actual requirements and international standards to ensure optimal production environments and air quality.

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