A cleanroom is an enclosed space in which the concentration of airborne particles is held below a defined limit. It is classified by that limit, priced by the square foot to build, and carries an operating cost for every year it stays in service. This page covers how one works, how the classes are graded, which industries require them, what they cost, and which step in microfluidics fabrication requires one.
Contamination control in a cleanroom is achieved mainly through air handling. Filtered air is supplied continuously and replaced faster than the occupants and the processes inside can introduce particles. Gowning and entry protocols support that objective.
HEPA filters in the ceiling supply air downward through the room and out through returns. An ISO 7 room runs 60 to 90 air changes an hour, which replaces the full volume of the room roughly once a minute while it is in service.
The room is held at a higher pressure than the space around it, so air escapes outward through any leak rather than drawing unfiltered air in. Surfaces are sealed and coved so that particles have nowhere to settle and every surface can be wiped down.
People are the largest source of particles in an operating cleanroom. Gowning, airlocks, and entry procedures exist to limit that contribution, which is also why cleanroom work is slower than bench work and why operators require training.
ISO 14644-1 classifies a cleanroom by the maximum number of particles of a given size permitted in one cubic metre of air. A lower class number denotes a cleaner room, and each step down the scale is a factor of ten. The four classes below are the ones encountered most often.
| Class | Max particles 0.5 micron and larger, per m³ | Where it is used |
|---|---|---|
| ISO 5 | 3,520 | Aseptic filling zones, isolators, fine photolithography |
| ISO 6 | 35,200 | High containment work, staging for sterile material, photolithography |
| ISO 7 | 352,000 | Medical device manufacturing, biotech research, general microfabrication |
| ISO 8 | 3,520,000 | Component preparation, assembly, packaging, background zones |
Particle limits per ISO 14644-1:2015, as tabulated by GMP Insiders. The standard also sets limits at other particle sizes; 0.5 µm is the size most often quoted. ISO 7 and ISO 8 correspond to the former US federal classes 10,000 and 100,000, which remain in common use.
Two conditions drive the requirement: the product has features smaller than a typical airborne particle, or contamination in the product reaches a patient. Beyond that, the difference between industries is how strict the limit has to be.
Feature sizes are far smaller than a typical airborne particle, so a single particle in the wrong place renders a die unusable. Semiconductor manufacturing is where the discipline originated.
Contamination in the product reaches a patient, so the environment is regulated rather than recommended, and the room has to be validated and revalidated on a defined schedule.
Products that are implanted or that enter the sterile field are manufactured in a controlled environment. This is the most common reason a device company operates an ISO 7 room.
The product is a living material and cannot be terminally sterilized after manufacture, so contamination control has to take place during the process itself.
A particle trapped beneath a coating or inside a sealed assembly is a permanent defect in a component that is expensive and often cannot be reworked.
Photolithography patterns features at the micron scale, so the same condition applies as in semiconductor manufacturing. This is the category microfluidics falls into, and it is covered below.
Making a PDMS chip splits into two halves. The first builds a master mold and needs a controlled environment. The second casts chips against that master and does not.
Photolithography patterns features at the micron scale. A particle settling on the photomask or on the resist during exposure blocks or distorts a feature. Because the master is a mold rather than a finished product, that defect is then reproduced in every device cast from it, which is why the environment matters more at this one step than anywhere downstream.
No single class is mandated for master fabrication. The requirement is set by the finest feature on the wafer. Fine geometry is typically run at ISO 5 to ISO 6, the same classes used for semiconductor work and implantable device manufacturing. Channels in the tens of microns, which covers a large share of ordinary microfluidic work, are commonly run at ISO 7. Less demanding geometry is made in a standard laboratory using a laminar flow hood over the steps where the wafer is exposed.
The requirement reflects established practice rather than physical necessity. Masters have been fabricated outside a cleanroom using dry film photoresist in an improvised room under ambient light, an approach developed specifically because conventional methods require expensive instrumentation and a cleanroom setting, and features down to 5 microns have been replicated from masters made without one. The relevant point is that the step generates workarounds at all. Alternatives exist, and they carry their own tradeoffs in resolution and repeatability.
In either case the master is what brings the room into the process. A method that does not require a master does not require the room, or the time needed to build one.
See the full PDMS process, step by step, with what each stage costs →
Two variables drive the figure: the classification the room has to hold, and whether it is a prefabricated system installed in an existing space or a room constructed in place. Published figures differ on that basis, so both are shown.
| Class | Prefabricated, per sq ft | Constructed, per sq ft |
|---|---|---|
| ISO 8 | $100 – $250 | $250 – $450 |
| ISO 7 | $250 – $450 | $400 – $650 |
| ISO 6 | $450 – $700 | Not published |
| ISO 5 | $700 – $1,000 | Not published |
Prefabricated figures as published by Labs USA; constructed figures as published by Terrapin Consulting Group for 2026. Both sources describe these as estimates that move with build method, region, and fit out.
The per square foot figure covers a compliant empty shell. Pass throughs, air showers, and gowning rooms are quoted separately at $5,000 to $25,000 each. Where the room falls under pharmaceutical good manufacturing practice, validation adds a further 8 to 18 percent on top of construction, covering particle counting, recovery testing, airflow visualization, and the documentation package. Process equipment is additional.
A cleanroom carries an ongoing cost as well as a capital one. Air handling is the largest component: HVAC and filtration account for 35 to 55 percent of the build budget, which indicates where the running cost concentrates. Filter replacement, preventive maintenance, and recertification apply for every year the room stays in service. Published annual figures vary widely by size, region, and classification, so no single figure is quoted here. The cost is fixed rather than variable, and applies regardless of output.
Feature and validation figures as published by Labs USA and Terrapin Consulting Group.
Controlled environments are necessary and well understood, and nothing here is an argument against them. In microfluidics the requirement attaches to master mold fabrication rather than to the chip itself. That is the step we removed.
See what we built instead