CADR stands for Clean Air Delivery Rate. CADR helps tell you how much of a particular contaminant is removed from the air within a specific period of time, and it creates an objective rating that allows consumers to compare one air purifier to another based on standardized testing. There are 3 pollutants that CADR measures, which are representative of different size particles, and they are: POLLEN, which represents larger particles (20 microns); DUST, which represents medium sized particles (5 microns); and SMOKE, which represents some of the smallest particles (0.1-1 microns). Since CADR represents the filtered airflow, this can be translated to understand square footage for a room size to be cleaned as well as necessary air changes per hour. The higher the CADR numbers, the better the overall ability of the unit to clean your indoor air and the faster the air in the room will be cleaned. You want to be most concerned with the smoke CADR number since that rating represents the removal of the smallest and most dangerous particles.