FFUs (Fan Filter Units) combine fan and filter (HEPA/ULPA) in ceiling-mounted units providing laminar airflow in cleanrooms. Design: Self-contained unit with fan, filter, and housing. Modular, replaceable. Mounted in cleanroom ceiling grid. Function: Draw air from plenum above ceiling, filter through HEPA/ULPA, discharge vertically downward into cleanroom at controlled velocity. Laminar flow: Provides uniform vertical airflow (0.3-0.5 m/s typical). Particles swept down to floor and exhausted. Coverage: Continuous FFU coverage in ISO Class 5 and cleaner. Partial coverage acceptable for less critical areas. Filter options: HEPA (99.97%) or ULPA (99.999%) depending on cleanliness requirement. Specifications: Airflow velocity, noise level, power consumption, pressure drop, filter efficiency. Maintenance: Filter replacement (1-3 years typical), fan motor service, pressure monitoring. Advantages: Modular installation, individual unit replacement, uniform coverage. Energy consideration: Significant energy consumer in fab. Energy-efficient EC motors and variable speed drives help. Manufacturers: AAF, Camfil, Nitta, Nippon Muki. Critical cleanroom infrastructure.