Compatible with PureProtect Water 3400 Series Replacement humidifier filter for Philips PureProtect 3400 Series, 2-in-1 air purifier/humidifier: AC3420, AC3421. Your air purifier model is indicated on the bottom of the appliance. Can be used for up to 6 months This humidifier filter provides long-lasting protection - optimal filtration - for up to 6 months (2). Philips original filter for optimal performance The original Philips filter has been specially developed for your appliance. For optimum performance, always use the Philips original filter. Hygienic humidification with NanoCloud technology NanoCloud emits an ultra-fine spray mist that is invisible to the naked eye. The technology humidifies air with up to 99.9 % less bacteria than conventional ultrasonic humidifiers. Safe to use with tap water (1). Connection with the Air+ app for more convenience Connect your device to the Air+ app and easily order replacement filters when needed.