Ventilation filters protect the patient, staff and equipment from microbial contamination by filtering both expiratory and inspiratory air. They are able to effectively filter out all types of particles and bacteria from the breathing gas. Ventilation filters are used in anesthesia, intensive care and emergency medical services and have a filter efficiency of up to 99.99995 %.

They also serve as heat and moisture exchangers and are therefore also known as HME filters (Heat and Moisture Exchanger). Over-humidification of breathing gas is prevented as the filter only stores the moisture from the expired air and releases it again during inspiration.