ISO 5/Class 100 is a cleanroom classification standard defined by ISO 14644-1 and the older US Federal Standard 209E. It specifies that the environment must contain no more than 3,520 particles per cubic meter of air, each particle being 0.5 microns or larger. This level of cleanliness is essential in industries like semiconductor manufacturing, pharmaceuticals, and biotechnology, where even microscopic contaminants can compromise product quality or safety. The standard ensures strict control over airborne particulates, achieved through specialized filtration, airflow, and operational protocols. ISO 5/Class 100 cleanrooms are among the cleanest environments, supporting critical processes that require extreme contamination control.