Warm mist humidifiers allow for the highest moisture saturation level, meaning the maximum amount of water vapor in the air. At the same time, warm mist humidifiers bring moisture to the air while killing most bacteria with steam. On the other hand, cool mist humidifiers use filters to remove impurities and operate more quietly. In our list of the Best Baby Humidifiers, four of our Top Picks are cool mist humidifiers.