HME stands for Heat and Moisture Exchanger. This cartridge-like component offers just that, and makes CPAP use much more comfortable with use. These HME units are compatible with the Transcend Micro CPAP adapter piece, and should be changed out on a weekly basis. If you want the easiest way to maintaining a healthy replacement regimen, try selecting "Subscribe and Save" with your check-out. Otherwise, the Transcend Micro AirMist HMEs come in a 4-pack; an 8-pack; and a 12-pack.