The HME (Heat and moisture exchanger) filter is one kind of ventilation circuit accessory that takes advantage of the patient's own body temperature and hydration levels to achieve effective humidification during successive breaths. The HME filters conserve the heat and moisture recovered from the exhaled air, which is then utilized during the inspiratory phase. Apart from the commonly used HME and HMEF filters, tHME and nHME filters are also available and have a broader range of applications.