Nispira HME filter is an inline humidification solution unit for use with ALL CPAP & BiPAP Machines and CPAP Masks. It is a waterless humidification that requires no additional power and takes up very little space. A great alternative to large humidifiers. The HME Humidifier Filter for CPAP & BiPAP therapy capture the heat and moisture from the air and exhalations, preserving and increasing humidity to prevent your airways from drying out. HME Filters are a great option for travel. Just simply attach the HME between your mask and your standard CPAP or BiPAP tubing. After that, turn on your machine and experience a steady flow of humidified sleep therapy air. HME Filters should be changed about once a week for best results. Outer diameter on both ends: 25mm / 22mm. A pack of 6 filters included.