ISO/TS 21220:2009 presents test methods and specifies a test rig for measuring the filter performance of particulate air filters used for general ventilation. The test rig is designed for an air flow rate of between 0,25 m³/s [900 m³/h (530 ft³/min)] and 1,5 m³/s [5 400 m³/h (3 178 ft³/min)].

ISO/TS 21220:2009 is applicable to air filters having an initial efficiency of less than 99 % with respect to 0,4 m particles. Filters in the higher end and those with an above 99 % initial efficiency are tested and classified according to other standards.

It combines two test methods: a “fine” method for air filters in the higher efficiency range and a “coarse” method for filters of lower efficiency. In either case, a flat‑sheet media sample or media pack sample from an identical filter is conditioned (discharged) to provide information about the intensity of the electrostatic removal mechanism. After determination of its initial efficiency, the untreated filter is loaded with synthetic dust in a single step until its final test pressure drop is reached. Information on the loaded performance of the filter is then obtained.

The performance results thus obtained cannot alone be quantitatively applied to predict in‑service performance with regard to efficiency and lifetime, so other factors influencing performance are also presented.