HEPASilent replacement filter for Blueair 201, 203, 270E and 303 air purifiers. The HEPA filter is made of a coat of fibers which are spaced out by 0.3 microns maximum, acting as a membrane catching harmful particles. The HEPA filtration technology was developed by the Committee of American Energy. The first HEPA filter was created in the 40s and used in the "Manhattan Project" to avoid contaminant leaks. These products have been perfected and improved to satisfy the increasing demand of air quality improvement in numerous technological industries, as the aerospace industry, the pharmaceutical industry, hospitals and the electronics industry (more precisely for microchip plants). An ULPA filter (Extreme Reactionary Low Penetration Air) can remove dusts, pollens and bacteria from the air with a 99.999% efficiency.