A static electric charge (positive or negative), or having a charge which remains local and permanent. This property does not diminish or disappear over time, and is not an additive that can wash out from air filter media, nor is it created by the addition of high voltage electricity. Airborne particles are attracted to the air filter media like iron filings to a magnet. Particles remain attached to the media until they are rinsed away.
Electrostatic air filters do not need to be plugged in to an outlet. The static charge is inherent in the air filter media.