The ResMed H4i™ Heated Humidifier is made to deliver 30% more heated humidification than previous humidifiers. The H4i™ Humidifier is to be used with ResMed S8 & S8 II CPAP Machines. The H4i is used to reduce dry nose/mouth, congestion or irritation sometimes caused by CPAP therapy. The humidifier produces warm, moist air making your CPAP use much more comfortable.