What Is a Cleanroom? The Basics You Need to Know

Think about the phone in your pocket or the medicine in your cabinet. Chances are, they were made in a cleanroom. But what is a cleanroom, and why are they needed?

Far from ordinary workspaces, cleanrooms are environments designed to control particles, temperature, humidity, and more, ensuring absolute precision where it matters most. From pharmaceuticals to aerospace, they make modern manufacturing possible in ways most people never see.

Let’s explore how cleanrooms work, what makes them unique, and why they’re critical to some of the world’s most important industries.

What Is a Cleanroom?

A cleanroom is a specially designed, controlled environment that limits the number of airborne particles, such as dust, microbes, aerosol particles, and chemical vapors.

These rooms are essential for industries where even microscopic contamination can ruin products or compromise research, such as in pharmaceuticals, electronics, aerospace, and biotech.

Cleanrooms are defined not just by how clean they are, but by how clean they stay, even as people work inside them, machines operate, and materials are brought in and out.

They maintain extremely low levels of particulate matter through stringent air filtration systems, controlled airflow, and precise environmental monitoring. Every square inch is engineered to reduce contamination and promote high product purity and safety.

How Clean Is a Cleanroom?

To appreciate the level of cleanliness in a cleanroom, consider this:

• A typical indoor room (such as an office or living room) has about 500,000 to 1,000,000 particles of 0.5 microns or larger per cubic foot of air.
• A Class 100 cleanroom (also called ISO Class 5) has no more than 100 particles of 0.5 microns or larger per cubic foot of air.

That’s not just cleaner, it’s several orders of magnitude cleaner.

To put it in perspective, a single human hair is about 70 microns wide. A 0.5-micron particle is 140 times smaller, invisible to the naked eye but potentially catastrophic in high-precision environments like semiconductor manufacturing or pharmaceutical compounding.

Cleanroom Classifications

So, how do we quantify this level of cleanliness?

Cleanrooms are classified by how many particles of a specific size are allowed in a given volume of air. The two most widely used systems are ISO 14644-1, the current international standard, and the older Federal Standard 209E, which is still commonly referenced in the U.S.

ISO 14644-1 (Current International Standard)

This system rates cleanrooms from ISO Class 1 (the cleanest) to ISO Class 9 (similar to ordinary indoor air). It measures airborne particles at multiple sizes (0.1 µm, 0.2 µm, 0.3 µm, 0.5 µm, 1 µm, and 5 µm) providing a comprehensive picture of air cleanliness.

Here’s a simplified snapshot of particle limits per cubic meter of air:

For a more technical dive, ISO 14644-1 defines cleanroom classes based on the concentration of particles per cubic meter at a specified particle size. Here's a simplified example:

Federal Standard 209E (Older, Still Common in the U.S.)

Before ISO became the global standard, cleanrooms in the U.S. were often classified by Federal Standard 209E, which focused on particles ≥0.5 microns per cubic foot of air.

Although FS 209E was officially retired, many industries, especially in the U.S., still use these terms due to familiarity and simplicity.

Core Features of a Cleanroom

To maintain extremely low levels of contamination, cleanrooms rely on several engineering and operational features:

1. High-Efficiency Filtration

At the heart of every cleanroom is its air filtration system. Cleanrooms use HEPA (High-Efficiency Particulate Air) or ULPA (Ultra-Low Penetration Air) filters to scrub incoming air of particles.

• HEPA filters remove 99.97% of particles ≥0.3 microns.
• ULPA filters remove 99.9995% of particles ≥0.12 microns.

This clean, filtered air is introduced through ceiling vents and directed in a controlled laminar flow pattern, either vertically or horizontally, sweeping particles away from critical work areas.

But clean air isn’t just a nice-to-have, it’s the very foundation of cleanroom performance. Particle control is non-negotiable. Even microscopic dust can cause defects, compromise safety, or invalidate test results.

High-efficiency filtration ensures that cleanrooms can meet strict cleanliness classifications and deliver the precision and reliability these industries demand.

2. Air Changes per Hour (ACH)

Air Changes per Hour (ACH) refers to how often the entire volume of air in a cleanroom is replaced within a single hour. Depending on the required cleanliness level, this can range from 20 changes per hour in less stringent environments to over 600 in ultra-clean spaces like ISO Class 1.

Without high ACH rates, even minor contamination events could quickly escalate, undermining product integrity and regulatory compliance. Frequent air exchange keeps the cleanroom environment stable, predictable, and safe for sensitive processes.

3. Pressure Differentials

A crucial but often invisible feature of cleanroom design is pressure control. Most cleanrooms are maintained at a higher air pressure than surrounding spaces. This is called positive pressure.

When a door opens, the higher pressure inside causes clean, filtered air to flow outward. This prevents unfiltered air and contaminants from entering the cleanroom.

Some specialized cleanrooms, such as those handling hazardous materials or pathogens, operate under negative pressure. In these cases, air is pulled inward to contain contaminants and keep them from escaping into adjacent areas.

Why does this matter? Even the most advanced filtration and strict protocols cannot eliminate every risk of contamination. Pressure differentials act as a safeguard. They create an invisible barrier that either protects the cleanroom from outside contamination or protects the outside world from what is inside.

Maintaining proper pressure is essential for ensuring cleanrooms function as controlled, secure environments, no matter their purpose.

4. Specialized Materials and Finishes

Every surface in a cleanroom is chosen with contamination control in mind. Materials that shed particles or harbor microbes are strictly avoided.

Instead, cleanrooms are built using smooth, non-porous materials like:

• Stainless steel
• Powder-coated metal
• Acrylic or PVC wall panels
• Epoxy-coated floors

These surfaces are durable, non-shedding, and designed to withstand frequent cleaning with disinfectants.

Smoothness is key. It prevents particles from becoming trapped in cracks or crevices and makes it easier to remove dust, microbes, and residues during cleaning routines.

In short, the materials used in a cleanroom are not just structural. They are an active part of the contamination control system. Every wall, ceiling, and floor helps maintain the clean, controlled environment these spaces are built for.

5. Cleanroom Protocols

Cleanroom performance depends not only on engineering, but also on the behavior of the people inside. Personnel must follow strict protocols every time they enter and work within the space.

These procedures often include gowning in sterile garments such as coveralls, masks, gloves, and booties. Some cleanrooms also require the use of air showers or sticky mats to remove particles from skin, clothing, and shoes before entry.

Inside the cleanroom, movement is minimized. Talking, walking, and operating equipment are all potential sources of contamination, so every action must be deliberate and controlled. Surfaces are cleaned frequently, sometimes several times a day, to remove particles and residues.

Even a properly gowned and trained person can release tens of thousands of particles per minute just by walking or speaking. Protocols exist to limit this risk as much as possible.

Without strict procedures, even the most advanced cleanroom design cannot maintain the required level of cleanliness.

Who Uses Cleanrooms?

Cleanrooms are essential wherever the slightest contamination could cause failure, contamination, or danger. Here are some key industries that rely on cleanrooms:

1. Pharmaceuticals and Biotechnology

Pharmaceutical and biotech companies rely on cleanrooms to ensure sterile, controlled environments for drug development and manufacturing. This is especially critical for products like vaccines, injectables, and biologics, where even microscopic contamination can compromise safety or effectiveness.

Cleanrooms protect these products from bacteria, fungi, and particles during sensitive steps like formulation and aseptic filling. To comply with FDA regulations, companies must follow strict cleanroom classifications under Current Good Manufacturing Practices (cGMP).

These standards are not just about compliance, they are about patient safety. A single contaminant in a sterile drug can mean the difference between healing and harm.

2. Semiconductors and Microelectronics

Semiconductor manufacturing demands extreme precision. Modern computer chips have features just a few nanometers wide. At that scale, a single speck of dust can ruin an entire batch of components, causing defects, delays, and massive losses.

To prevent this, production facilities operate in ultra-clean environments, often rated ISO Class 1 to Class 3. These are among the cleanest spaces in existence, even cleaner than hospital operating rooms.

Companies like Intel and TSMC invest heavily in cleanroom technology because particle control is essential. Without it, they could not produce the powerful and reliable electronics that power everything from smartphones to satellites.

3. Aerospace

In aerospace, cleanrooms are used to assemble spacecrafts, satellites, and precision instruments to protect them from dust, particles, and microbes that could interfere with performance in space.

Once launched, these systems cannot be repaired. A tiny particle on a lens or sensor can cause mission failure. That is why facilities like NASA’s Jet Propulsion Laboratory maintain some of the highest-class cleanrooms in the world.

Cleanrooms also help control bioburden, which is the presence of Earth-based microbes. This prevents unintended contamination of other planets during space exploration.

4. Food and Beverage

While not as common as in pharmaceuticals or electronics, cleanrooms play an important role in high-risk areas of food production. Products like baby formula, ready-to-eat meals, and medical nutrition must be manufactured under tightly controlled conditions to prevent contamination.

Cleanrooms in food facilities help reduce exposure to airborne bacteria, mold, and dust that could lead to spoilage or foodborne illness. They are especially important when the product will not be cooked before consumption.

These controlled environments support extended shelf life, product consistency, and consumer safety. In some cases, cleanroom use can also help companies meet strict export or regulatory standards.

Practical Takeaways

Cleanrooms aren’t just for space shuttles and semiconductor labs, they’re essential to everyday products we rely on. By keeping airborne particles, microbes, and contaminants under control, cleanrooms protect the integrity of critical processes across dozens of industries.

If your organization is planning a new cleanroom or upgrading an existing one, here are a few key takeaways to keep in mind:

• Start with the end in mind. Cleanroom classification requirements should drive decisions around layout, filtration, airflow, and surface materials.
• Filtration is the foundation. HEPA and ULPA filters aren’t just accessories, they’re central to maintaining ISO compliance and protecting your process.
• Maintenance matters. A cleanroom is only as effective as its upkeep. Regular inspections, filter replacements, and airflow testing are essential for long-term performance.

Understanding these principles is the first step toward building a space that performs the way you need it to. But knowing what’s required and actually implementing it are two very different things, and that’s where expert support makes all the difference.

Our cleanroom services cover everything from design and build to filtration and ongoing maintenance. Whether you're starting from scratch or optimizing an existing space, we can help you meet the highest standards for clean air.