There are many ways to compare air purification systems, whether it be how thoroughly the purifier cleans air, what types of pollutants it removes, how energy efficient it is, and what room size you can put the air purifier in. The most common measure of comparison is a number called the CADR (Clean Air Delivery Rate), which is used to describe an air filter's ability to remove all pollutant particles, and is usually expressed in cubic feet per minute (CFM). The CADR of the Puritii APS is 303 CFM. This rating is typically only reported for the highest fan speed, in this case Turbo setting. Comparisons can also be made for the number of filtration stages (the Puritii APS has 11, most competitors advertise 3-5) and what type of pollutants the filtration stages remove (the Puritii APS removes all three types of pollutants - particulates, VOCs, bioaerosols - with high efficiency, whereas many commercial products focus only on particulate and odour removal).