Rowenta XD6085 NanoCaptur Filter Formaldehyde Remover for PU4020 Intense Pure Air Bedroom Auto Purifier Patented Rowenta NanoCaptur technology destroys permanently formaldehyde emitted by : cleaning products, pressed wood materials, building materials Formaldehyde is considered as the most dangerous home pollutant according to the world Health organization The NanoCaptur yellow granules inside the filter turn red if saturated, meaning it is the time to replace the filter Fits PU4020 Intense Pure Air purifier - room coverage up to 400 sq. ft. Replace on an average once a year - always monitor color of the granules if brown need to replace the filter