This is a replacement air filter for the Medquip Airial and Medquip Airial Compact Nebulizer (models MQ5800 and MQ5900 manufactured after 2013). It is important to regularly replace the air filter to keep your nebulizer machine running in top condition. Filters should be replaced every 30 days, or when it becomes dirty or gray. Comes in a bag of 5 filters.