Ultra-low particulate air
Ultra-low particulate air (ULPA) is a type of air filter. A ULPA filter can remove from the air at least 99.999% of dust, pollen, mold, bacteria and any airborne particles with a minimum particle penetration size of 120 nanometres (0.12 μm, ultrafine particles).
Source: Wikipedia — Ultra-low particulate air (CC BY-SA 4.0)