What Is a Cleanroom? Definition, How It Works and What's Used Inside
Published by Harmony Lab & Safety Supplies on Apr 02, 2026
Updated November 2026
A cleanroom is a room where the number of airborne particles is kept below a set limit. That limit is defined by an ISO 14644-1 class, from ISO 1 (cleanest) to ISO 9. A cleanroom reaches its class with HEPA-filtered air, controlled airflow and pressure, and strict rules for the people, materials and supplies that go inside.
Cleanroom vs Controlled Environment
| Cleanroom | Controlled environment | |
|---|---|---|
| What's controlled | Airborne particle count, plus usually pressure, temperature and humidity | Any mix of temperature, humidity, pressure or access |
| Classified to a particle limit | Yes, an ISO 14644-1 class (for example ISO 7) | Not necessarily |
| Gowning and approved supplies | Required, stricter at cleaner classes | Varies by site |
| Examples | Semiconductor fab, sterile compounding room, medical device assembly | Server room, storage area, some labs |
Every cleanroom is a controlled environment, but not every controlled environment is a cleanroom.
How a Cleanroom Works
- Filtered air: supply air passes through HEPA or ULPA filters. A HEPA filter removes at least 99.97% of particles 0.3 microns in size, the hardest size to catch (EPA, citing the Department of Energy definition).
- Airflow and air changes: clean air sweeps particles toward the returns, where they are filtered out. Cleaner classes need more air and more uniform airflow.
- Pressure: most cleanrooms are kept at a higher pressure than the rooms around them, so air leaks out, not in.
- People and materials: people shed particles constantly, so gowning, airlocks, adhesive mats and approved wipes, paper and pens keep contamination from coming in with them.
Cleanroom Classes at a Glance
| ISO class | Max particles ≥0.5 µm per m³ | Old FS 209E name |
|---|---|---|
| ISO 5 | 3,520 | Class 100 |
| ISO 7 | 352,000 | Class 10,000 |
| ISO 8 | 3,520,000 | Class 100,000 |
See the full cleanroom classification chart for ISO 1–9, other particle sizes and EU GMP grades.
Who Uses Cleanrooms
- Pharmaceutical and biotech manufacturing, and sterile compounding pharmacies
- Medical device assembly and packaging
- Semiconductor and electronics, where one particle can ruin a chip
- Aerospace and optics, and precision assembly
- Research and testing labs
What's Used Inside a Cleanroom
| Supply | Why it matters | Shop |
|---|---|---|
| Cleanroom gloves | Keep skin oils and particles off product | Cleanroom gloves |
| Coveralls, hoods and boot covers | Contain the particles people shed | Cleanroom coveralls |
| Face masks | Limit particles from breathing and talking | Cleanroom face masks |
| Wipes, dry and presaturated | Low-lint cleaning and surface prep | Cleanroom wipes, presaturated wipes |
| Swabs | Cleaning small parts and tight spots | Cleanroom swabs |
| Paper and notebooks | Low-particle documentation | Cleanroom paper |
| Adhesive mats | Catch particles on shoes and carts at the entrance | Adhesive mats |
For procedures, see our cleanroom gowning guide and cleanroom cleaning procedure.
Frequently Asked Questions
What is the purpose of a cleanroom?
To keep particles and other contamination from damaging products or processes that are sensitive to them.
Is a cleanroom sterile?
Not by itself. A cleanroom limits particles. Sterility needs separate processes, such as aseptic technique, disinfection and sterilization.
What does ISO 5 mean?
No more than 3,520 particles 0.5 microns or larger per cubic meter of air, the same as the old Class 100.
What's the cleanest cleanroom class?
ISO 1.
Sources: ISO 14644-1:2015, Cleanrooms and associated controlled environments, Part 1: Classification of air cleanliness by particle concentration; EPA, What is a HEPA filter?