A Class 100,000 cleanroom—designated as ISO 8 under current global standards (ISO 14644-1)—is a controlled environment engineered to maintain a maximum particle count of 100,000 particles (0.5 microns or larger) per cubic foot of air.
For perspective, typical indoor office air contains between 500,000 to over 1,000,000 particles per cubic foot, meaning a Class 100,000 cleanroom is roughly 5 to 10 times cleaner than standard ambient indoor air.