The HumidX - AirFit F20 is a unique product that is specifically designed to be used with the AirFit F20 mask. It is important to note that this product is not compatible with any other type of mask and must be replaced within 30 days of opening in order to ensure optimal performance. This product is essential for those using the AirFit F20 mask, as it helps to reduce dryness and irritation that can be caused by using a CPAP mask.