What ISO Class corresponds to ULPA filters?

• A. Class 7
• B. Class 9
• C. Class 3
• D. Class 5

Answer: (C)

ULPA filters deliver ultra-high filtration efficiency, typically capturing at least 99.999% of particles as small as 0.12 μm. ISO cleanroom classifications define how clean the air must be, with lower ISO numbers (like ISO Class 3) representing far more stringent particle limits than higher numbers. Because ULPA filters achieve such extremely low particle counts, they map to the most stringent end of the ISO scale, which is ISO Class 3. In practice, HEPA filters are often associated with less stringent classes (such as ISO Class 5), while ULPA can achieve the tighter ISO Class 3 requirements needed for the cleanest environments.