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Cleanroom Classifications: Everything You Need to Know

Cleanrooms are synthesized environments with various degrees of contamination control to suit various industries.

The concept of “clean” here goes well beyond regular cleaning; it includes controlling the airflow and preventing contaminants from entering the room through certified filters and other equipment.

This post will serve as your complete guide to cleanroom classifications. We’ll show you how they are officially classified, how they used to be classified, the types of classifications, and everything in between. 

What Is Cleanroom Classification?

Cleanroom classification provides a standardized way to categorize controlled environments based on their level of air cleanliness, specifically measuring the concentration of airborne particles

This classification system serves as a universal language that helps industries maintain consistent quality standards across different facilities and applications. 

The primary objective of the classification is to measure the maximum number of particles of specific sizes allowed per cubic meter of air.

For example, when we measure particles that are 0.5 micrometers or larger (about 1/200th the width of a human hair), we can determine if a cleanroom meets particular classification requirements.

The measurements become increasingly stringent as we move up the classification scale, with Class 1 being the cleanest and most tightly controlled environment. 

How Clean are Cleanrooms?

We’ll explain the classes in detail soon enough, but for now, let’s see just how different a cleanroom is compared to a regular room to put things into perspective.

Let’s say that we have a typical office environment in which the air contains roughly 35 million particles per cubic meter. In comparison, the Class 1 cleanroom example we mentioned earlier contains only 10 particles per cubic meter. 

In other words, a cleanroom’s air is 350,000,000% cleaner compared to your typical office environment. 

Such cleanliness is achieved through many specialized control methods (which we’ll also discuss) to keep airborne particles at such low levels to maintain an adequate environment for microscopic industries. 

Understanding Cleanroom Standards

Cleanroom standards serve as the foundation for designing, operating, and maintaining controlled environments across industries. These standards provide precise specifications for air cleanliness, testing methods, and operational procedures. 

Currently, and as of 2025, the most widely used classification system is ISO 14644-1, which replaced the older US Federal Standard 209E. However, the 209E isn’t obsolete, at least unofficially, as you can still hear people reference that system. 

Accordingly, we’ll discuss each. 

ISO 14644: The Global Benchmark

The International Organization for Standardization (ISO) developed ISO 14644 as a comprehensive framework for cleanroom classification and testing.

This standard can be divided into six primary parts. They are as follows:

  • Classification System Overview
  • Technical Requirements and Measurements (Particle Size Considerations)
  • Testing and Verification Methods (Airborne Particle Count Testing)
  • Classification States
  • Documentation and Compliance Requirements
  • Impact on Industry Practices

Classification System Overview

The ISO classification system defines nine classes, ranging from ISO Class 1 (most stringent) to ISO Class 9 (least stringent).

Each class specifies the maximum allowable concentrations of particles at defined sizes, measured in particles per cubic meter (C2).

The standard uses a logarithmic scale, where each subsequent class allows approximately ten times more particles than the previous one. 

Technical Requirements and Measurements (Particle Size Considerations)

The standard measures particles in six size ranges:

  • 0.1 µm
  • 0.2 µm
  • 0.3 µm
  • 0.5 µm
  • 1.0 µm
  • 5.0 µm

Each size category has specific concentration limits depending on the ISO Class. For example, in ISO Class 5, the maximum allowable concentration for particles ≥0.5 µm is 3,520 particles per cubic meter, while for particles ≥5.0 µm, it’s only 29 particles per cubic meter.

Here’s what it looks like in all classifications, along with the types of materials typically synthesized in each:

ISO Class≥0.5 µm (particles/m³)≥5.0 µm (particles/m³)Material Synthesis Types
1100.1Advanced semiconductor fabrication, nanotechnology, and aerospace.
21001High-precision optics, advanced pharmaceuticals, and microelectronics.
31,00010Electronics assembly, biotechnology research, and pharmaceutical manufacturing.
410,000100Medical device manufacturing, aerospace components, and cleanroom packaging.
5100,0001,000Pharmaceutical filling, semiconductor manufacturing, and tissue engineering.
61,000,00010,000Biopharmaceutical production, laboratory research, and medical device assembly.
710,000,000100,000General pharmaceutical production, electronics manufacturing, and food processing.
8100,000,0001,000,000Low-risk pharmaceutical operations and general industrial applications.
91,000,000,00010,000,000Non-critical environments like warehouses and general manufacturing.

Testing and Verification Methods (Airborne Particle Count Testing)

The standard mandates specific testing procedures using calibrated particle counters. These instruments must meet the requirements outlined in ISO 21501-4, ensuring measurement accuracy and consistency.

Testing typically involves:

  • Systematic sampling across designated locations
  • Statistical analysis of particle count data
  • Documentation of environmental conditions during testing
  • Regular calibration of measurement equipment

Classification States

ISO 14644 recognizes three distinct operational states:

  • As-built: Complete and ready for operation, but without equipment or personnel.
  • At-rest: Complete and ready for operation, along with all services functioning and equipment installed, but without personnel.
  • Operational: Normal operation with all services functioning and personnel present. 

Documentation and Compliance Requirements

Maintaining ISO 14644 compliance requires extensive documentation, including but not limited to:

  • Initial classification testing results
  • Periodic monitoring data
  • Equipment calibration records
  • Environmental parameter logs
  • Personnel training records
  • Standard operating procedures (SOPs)
  • Contamination control strategies

Impact on Industry Practices

1. Design Considerations

The standard influences critical design elements, which include: 

  • HVAC system specifications.
  • Air filtration requirements
  • Material selection for surfaces
  • Location or return air grilles
  • Room pressurization schemes
  • Placement of monitoring devices

2. Operational Protocols

Implementation requires strict operational controls, including:

  • Cleaning and sanitization schedules
  • Material transfer protocols
  • Personnel flow patterns
  • Defined gowning procedures
  • Maintenance schedules
  • Environmental monitoring programs

Federal Standard 209E

The Federal Standard 209E has been officially discontinued since 2001. However, it’s still historically significant and is still referenced in many existing facilities. That’s why it’s still worth explaining. 

It was developed in 1963 by the U.S. General Services Administration and has since served as the primary cleanroom standard until the adoption of ISO 14644. 

That being said, it’s still fairly common alongside ISO classifications, particularly in North American facilities. We’ll explain three primary aspects of it:

  • It’s classification
  • How it compares to the ISO 14644
  • Its Impact

Classification System Structure

This standard used a straightforward naming convention based on the maximum number of particles ≥0.5 µm allowed per cubic foot of air.

For example, Class 100 allowed 100 particles per cubic foot, while Class 100,000 allowed 100,000 particles per cubic foot.

The fact that the “naming” of each class already had the number of allowed particles was the reason why it was so easy to learn and why some facilities still use it despite being officially obsolete. 

Comparison with ISO 14644

Despite being easy to understand, the Federal Standard 209E focused primarily on 0.5 µm particle size, which made it less comprehensive.

Accordingly, we can only show you the conversion table of the 0.5 µm particles since it has no equivalent to ≥0.5 µm particles. 

That being said, here’s the conversion table:

ISO ClassFS 209E Class
11
210
3100
41000
510,000
6100,000
71,000,000
810,000,000 (approx.)
9100,000,000 (approx.)

In addition to the difference in the main focus on 0.5 µm particles, the 209E differed also in the following aspects:

  • Use of cubic feet rather than cubic meters, which was less universal
  • The limited consideration of larger particle sizes
  • The less comprehensive testing methodology

Legacy Impact

Despite its retirement, FS 209E influences modern cleanroom practices through:

  • Equipment specifications
  • Standard operating procedures
  • Existing facility classifications
  • Training materials
  • Industry documentation

Additionally, the transition from FS 209E to ISO 14644 has led to:

  • Dual classification listings in specifications
  • Revised documentation requirements
  • Modernized facility designs
  • Modified personnel training programs

Types of Cleanrooms 

The cleanroom industry offers several distinct configurations to match specific operational needs. Each type serves unique contamination control requirements while considering factors like budget constraints, available space, and maintenance capabilities.

The three options we have are modular, softwall, and hybrid cleanrooms. 

We’ll get detailed, but in short, modular cleanrooms are the more expensive option and the better choice if you need a durable, long-lasting cleanroom with high levels of customization and environmental control. 

On the other hand, softwall cleanrooms are a good choice if you need a more affordable, flexible, and easily installed solution, especially for temporary or less demanding applications.

You can guess by now that the hybrid combines the two. We’ll explain how exactly that happens in a moment. 

That being said, let’s get to the details:

1. Modular Cleanroom

A modular cleanroom is a controlled environment built from pre-manufactured components, similar to putting together building blocks.

Unlike traditional cleanrooms that require extensive construction, modular cleanrooms arrive as ready-made panels and parts that fit together to create a complete cleanroom.

This approach makes them particularly valuable for companies that need quick installation or might need to relocate their cleanroom in the future.

We’ll discuss the characteristics of modular cleanrooms through three primary aspects:

  • Core Components and Design
  • Environmental Control Systems
  • Industry Applications and Benefits

Core Components and Design

The fundamental element of a modular cleanroom is its panel system. These panels come pre-finished with smooth, cleanable surfaces and contain all necessary utility connections. 

When these rooms are assembled, they create walls that maintain strict air cleanliness while providing access to electrical, gas, and monitoring systems. 

The “modular” concept extends to every part of the cleanroom. For example, the ceiling grid arrives in sections, ready to accept filtration units and lighting. The flooring system includes pre-measured sections that create a seamless surface.

Even the air handling systems come as complete units that integrate directly with the wall and ceiling components. 

Environmental Control Systems

One of the best aspects of modular design is how it excels in maintaining consistent environmental conditions.

Each ceiling section houses precisely positioned high-efficiency particulate air (HEPA) or ultra-low particulate air (ULPA) filters that create a uniform, clean airflow.

The pre-engineered nature of these components ensures proper air circulation patterns, which, as we’ll explain later, is critical in maintaining cleanliness classifications. 

We also have a floor system that deserves special attention because it must meet multiple demands. It supports heavy equipment, prevents static buildup, and resists chemical damage.

The modular design allows for custom load-beating sections when needed without compromising the room’s overall cleanliness. 

Industry Applications and Benefits

Pharmaceutical industries, electronic manufacturers, and research laboratories often prefer modular cleanrooms. 

The pharmaceutical industry frequently chooses modular cleanrooms because they can be operational within weeks instead of months. Their pre-validated components speed up the certification process significantly. 

Electronics manufacturers value these rooms for their adaptability. As production needs change, the modular design allows for expanding or reconfiguring the space without extensive demolition or reconstruction. 

Research laboratories benefit from the modular approach when grant funding arrives and they need clean spaces quickly. The standardized components make it easier to maintain compliance with cleanliness requirements while staying within budget constraints. 

2. Softwall Cleanroom

A softwall cleanroom uses flexible, transparent plastic curtains or strips instead of rigid wall panels to create a controlled environment. This unique approach provides a more economical and space-efficient alternative to traditional cleanroom construction.

The “soft” walls typically consist of industrial-grade vinyl or polyethylene materials that meet cleanliness requirements while allowing visual monitoring of operations inside. We’ll discuss four aspects of these rooms: 

  • Structure and Materials
  • Advantages and Limitations
  • Practical Applications
  • Installation and Maintenance

Structure and Materials

The framework of a softwall cleanroom starts with a sturdy aluminum or stainless steel support structure. This skeleton supports both the ceiling grid system and the clear plastic curtains.

These curtains attach securely to the frame using specialized tracking systems that allow them to slide smoothly for access while maintaining proper sealing when closed. 

The ceiling construction mirrors traditional cleanroom design, incorporating HEPA filtration and lighting systems.

However, the flexible nature of the walls requires careful consideration of air pressure management to prevent billowing or improper air distribution patterns. 

Advantages and Limitations

Softwall cleanrooms excel in situations where quick setup and potential relocation might become necessary. Their lighter construction makes them ideal for temporary research projects or pilot production runs. 

The clear walls provide unobstructed views of the entire operation, which is useful when supervision is needed. 

However, these systems face certain operational constraints. They typically achieve classifications up to ISO 7, making them unsuitable for applications requiring more stringent cleanliness levels. 

The flexible walls also provide less protection against sound transmission and offer minimal insulation compared to rigid wall systems. 

Practical Applications

Small-scale medical device assembly operations often choose softwall cleanrooms for their cost-effectiveness. The same goes for research laboratories, which use them for short-term projects where a controlled environment is necessary but permanent construction isn’t justified. 

They’re also valuable for quality control departments, as they frequently install softwall cleanrooms for inspection processes. 

Lastly, educational institutions also favor these systems for teaching laboratories, where visibility and cost considerations are often needed. 

Installation and Maintenance

Setting up a softwall cleanroom often requires fewer resources than traditional construction.

The process involves assembling the frame, installing the ceiling grid with filtration units, and hanging the curtain walls. This simplified installation often eliminates the need for specialized construction crews or extensive facility modifications.

Maintaining these systems focuses primarily on regular cleaning of the curtain materials and ensuring proper tension in the tracking systems.

Plus the smooth surfaces of the curtains make them relatively easy to clean, though they require careful handling to prevent damage during the process. 

3. Hybrid Cleanroom

A hybrid cleanroom combines elements of both modular and softwall cleanrooms. The idea here is to balance the cost-effectiveness of softwall cleanrooms with the versatility of modular ones. 

We’ll discuss the characteristics of hybrid cleanrooms through these aspects:

  • Core Concept and Design
  • Considerations
  • Typical Applications

Core Concept and Design

The core idea behind a hybrid cleanroom is to leverage existing building infrastructure or conventional construction methods for certain parts of the cleanroom while utilizing modular components for critical areas that need higher levels of cleanliness or control. 

These rooms often utilize the already existing walls, ceilings, and floors of a building to significantly reduce construction costs and time.

Modular wall panels, ceiling grids with HEPA/ULPA filters, and specialized flooring are then integrated into the existing structure to create the controlled environment.

Hybrid cleanrooms often employ zoning strategies, where areas requiring higher cleanliness levels (e.g., critical processing zones) are constructed with modular components.

On the other hand, less critical areas (e.g., gowning rooms or storage areas) may utilize conventional construction or existing building features.

As for air circulation, HEPA/ULPA filtration units are carefully integrated into the hybrid design to ensure proper airflow and particle control. This typically involves a good amount of ductwork within existing walls or ceilings or the use of modular air-handling units.

Considerations

Besides saving time and money, hybrid cleanrooms are excellent because of their design flexibility. They allow for great adaptability when they integrate into existing building layouts and constraints.

However, there are a few considerations to keep in mind:

  • Integration Challenges: Integrating modular components with existing structures requires careful planning and coordination to ensure proper sealing, airflow, and compatibility.  
  • Cleanliness Limitations: While hybrid cleanrooms can achieve a range of ISO classes, achieving the highest levels (e.g., ISO 5 or lower) can be more challenging compared to fully modular designs due to potential limitations in sealing and airflow control within existing structures.
  • Modification Limitations: Modifying or expanding a hybrid cleanroom can sometimes be more complex than with a fully modular design, as it may involve extensive alterations to building infrastructure. 

Typical Applications

Hybrid cleanrooms are commonly used in various industries:

  • Pharmaceutical and Biotech: For less critical areas within manufacturing facilities or for research labs where high-level containment is not required throughout the entire space.
  • Electronics Manufacturing: For assembly or testing areas where some level of cleanliness is needed but not the ultra-high levels required for semiconductor fabrication.
  • Food Processing: For areas requiring hygienic conditions and some level of air cleanliness to prevent contamination. 

Factors Affecting Cleanroom Classification

We’ve already explained how particle size and quantity affect cleanroom classifications. However, there are five other factors that also influence the classification:

1. Air Filtration Systems

Effective air filtration is essential for maintaining cleanroom standards. Cleanrooms typically utilize HEPA filters or ULPA filters to remove particulates from the air.

The efficiency and type of filtration system directly impact the cleanroom’s ability to meet its designated classification.

2. Air Changes Per Hour (ACH)

The frequency of air changes is another critical factor in cleanroom design.

Higher ACH rates are necessary for cleaner classifications; for example, an ISO Class 7 cleanroom requires between 60 to 90 air changes per hour to maintain its standards.

This ensures that contaminants are continuously removed and replaced with filtered air.

3. Environmental Control Parameters

Temperature, humidity, and airflow patterns must be strictly controlled within a cleanroom. Variations in these parameters can lead to increased contamination levels and affect the performance of sensitive processes.

For instance, maintaining specific temperature and humidity levels can help prevent condensation and microbial growth.

4. Design and Construction Materials

The materials used in constructing a cleanroom, such as walls, ceilings, floors, and fixtures, play a significant role in its classification.

Smooth surfaces that are easy to clean reduce particle accumulation and contamination risks.

Additionally, the overall design must facilitate proper airflow and minimize dead zones where particles can settle.

5. Intended Use and Process Requirements

The specific applications for which a cleanroom is designed will dictate its classification requirements.

Processes that are more sensitive to contamination will necessitate higher cleanliness standards, influencing both the design and operational protocols within the cleanroom.

FAQs 

What Are Cleanrooms Used For?

Cleanrooms are used to control airborne particles and other contaminants in environments requiring high levels of cleanliness for manufacturing, research, or other sensitive processes in industries like pharmaceuticals, electronics, and aerospace.

What Does ISO Stand For?

ISO stands for the International Organization for Standardization, an independent, non-governmental international organization that develops standards to ensure quality, safety, and efficiency. 

What Is a Class 1 Clean Room?

A Class 1 cleanroom (according to older Federal Standard 209E, roughly equivalent to ISO Class 3) is the cleanest achievable environment with extremely low particle counts. It’s often used for highly sensitive applications.

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