HEPA stands for High-Efficiency Particulate Arrestance. To qualify for the standard, a HEPA filter must capture 99.99% of particulate matter down to 0.3 microns. The filter traps the smallest of particles while maintaining airflow. HEPA filters are the preferred filtration system for most sensitive manufacturing and healthcare situations. Measured in microns, wood dust is particularly troublesome to remove from an environment once it is airborne. Using a power tool connected to a vacuum fitted with a HEPA filter ensures a clean working environment and protects the user and those working nearby. It fits Festool CT vacuum extractors (not suitable for AutoClean extractors). Supplied in a pack of 2.