Published 09.22.25

Understanding the different cleanroom classifications and their gowning needs

When you're working in industries where even the smallest particles matter—pharmaceuticals, biotechnology, aerospace, microelectronics—cleanrooms become your fortress against contamination.

When you're working in industries where even the smallest particles matter—pharmaceuticals, biotechnology, aerospace, microelectronics—cleanrooms become your fortress against contamination. These specialized environments are carefully designed to keep unwanted particles at bay. The thing is, not every cleanroom needs the same level of protection.

The "cleanliness" level of your particular cleanroom determines everything about how it's built and, more importantly for daily operations, what you need to wear inside it. Cleanrooms can be non-aseptic (non-sterile), where the focus is on particle control, or aseptic (sterile), where contamination control extends to microorganisms and sterile practices are required.

So how do you know what level of clean you're dealing with? And what does that mean when you're getting ready to enter?

The science of clean: Understanding cleanroom classifications

Cleanroom classifications work by setting limits on how many airborne particles of specific sizes are allowed in a given volume of air. The cleaner the room needs to be, the fewer particles it can tolerate. It's a precise science governed by two main systems worldwide:

1. ISO 14644-1: This is the current global standard that most facilities use today. It runs from ISO Class 1 (the cleanest) to ISO Class 9 (the least stringent). The classification depends on number of particles equal to or larger than specified sizes (0.1 µm, 0.2 µm, 0.3 µm, 0.5 µm, 1.0 µm, and 5.0 µm) permitted per cubic meter of air.

  • Key takeaway: A lower ISO class number means a cleaner environment. For example, an ISO Class 5 cleanroom is significantly cleaner than an ISO Class 8.

2. Federal Standard 209E (FS 209E): While officially superseded by IS0 14644-1, this older system is still referenced in some older facilities or specifications, especially in the U.S. FS 209E classified cleanrooms from Class 1 to Class 100,000 based on particles per cubic foot of air.

  • Comparison: A "Class 100" cleanroom (FS 209E) translates to roughly an ISO Class 5, and a Class 10,000 to an ISO Class 7.

Why do classifications matter for gowning?

In most cleanrooms, people represent the largest source of contamination, shedding millions of skin flakes and thousands of microscopic hairs daily. Even talking or moving can generate particles. This is exactly why gowning requirements scale directly with cleanroom classifications. The stricter your classification, the more extensive and specialized your protective clothing needs to be.

Cleanroom classifications and their gowning needs

From basic to sterile: gowning across classifications

Let's break down the general gowning expectations for different ISO classes, moving from the least to the most stringent:

ISO Class 8 (Equivalent to FS 209E Class 100,000)

Basic environmental control

Applications: General manufacturing floors, packaging areas, non-sterile compounding

  • Contamination control focus: Primarily aims to control larger airborne particles.
  • Gowning needs:
    • Hairnet/Bouffant cap to contain hair
    • Beard cover to contain facial hair
    • Smocks, often knee-length, to cover street clothes
    • Shoe covers to prevent tracking in debris from outside
    • Gloves, typically non-sterile vinyl or nitrile, recommended for product handling

ISO Class 7 (Equivalent to FS 209E Class 10,000)

Controlled manufacturing

Applications: Medical device manufacturing, pharmaceutical preparation areas

  • Contamination control focus: Controls a wider range of particle sizes and demands more rigorous procedures.
  • Gowning needs: (in addition to ISO 8)
    • Full cleanroom suit/coverall made from low-linting material (e.g., polyester woven fabric) to cover the entire body. Often worn over scrubs or a designated cleanroom undergarment.
    • Hood to fully cover the head and neck, often tucked into the coverall.
    • Cleanroom-specific footwear – shoes or booties – to fully enclose the foot, never worn outside the cleanroom. Shoe covers may be used in conjunction with the dedicated footwear.
    • Gloves, often nitrile or latex and changed more frequently for the more stringent standards.

ISO Class 6 (Equivalent to FS 209E Class 1,000)

Precision manufacturing

Applications: Microelectronics assembly, precision component manufacturing

  • Contamination control focus: Extremely tight control over airborne particles, including smaller sizes.
  • Gowning needs: Similar to ISO Class 7, but garment quality is more critical. Greater emphasis on:
    • Higher quality cleanroom garments with more tightly woven fabrics to prevent particle shedding.
    • Gloves – double gloving is common.
    • Sterile garments may be introduced, particularly in pharmaceutical or biotech where aseptic conditions are critical.

ISO Class 5 (Equivalent to FS 209E Class 100)

Critical environments

Applications: Sterile drug manufacturing and medical device assembly, sensitive nanotechnology

  • Contamination control focus: Extremely strict control over all particle sizes, with a strong focus on preventing microbial contamination
  • Gowning needs: This is where gowning becomes highly specialized, often involving multiple layers and sterile items.
    • Sterile cleanroom suit/coverall typically individually packaged for further protection.
    • Sterile hood to cover head, neck, and shoulders, overlapping with the coverall.
    • Sterile gloves, often double or triple gloved.
    • Sterile cleanroom boots/booties extend up the leg, fully enclosing the cleanroom footwear.
    • Face mask/goggle to contain exhaled particles and protect eyes.
    • Low-linting cleanroom undergarments may be required beneath the suit.
    • Gowning technique involves a rigorous, multi-step procedure meticulously followed in dedicated gowning anterooms to prevent contamination during the donning process.

ISO Class 4, 3, 2, and 1

Applications: Advanced semiconductor manufacturing, specialized research

  • Contamination control focus: These are the most stringent cleanrooms, with the highest level of control over sub-micron particles.
  • Gowning needs: For these ultra-clean environments, personnel entry is often minimized entirely. When allowed, gowning is essentially a more rigorous version of ISO 5 and can include:
    • Air-fed suits – personal air filtration systems are integrated into the suits.
    • Full encapsulation gowning to provide a complete barrier between the person and the environment.
    • Even more meticulous gowning protocols with multiple stages and stricter contamination checks.

The importance of gowning protocol

Having the appropriate garments is only part of effective contamination control. The procedures for donning and doffing cleanroom clothing are equally critical. Improper gowning techniques can introduce more contamination than having no gown at all.

This is why facilities invest in rigorous training programs, dedicated anterooms, and detailed standard operating procedures (SOPs) – all non-negotiable in any classified cleanroom environment.

Choosing the right classification

Selecting the appropriate cleanroom classification requires balancing contamination control needs with operational requirements and costs. Over-specifying can lead to unnecessary expenses and operational complexity, while under-specifying risks product quality and regulatory compliance.

Understanding cleanroom classifications and their corresponding gowning needs is fundamental to maintaining product quality, ensuring research integrity, and safeguarding the health of personnel in critical environments. By matching the right garments to the right classification, industries can effectively combat contamination and uphold the highest standards of cleanliness.