ISO 16890 (2016) and ASHRAE 52.2 (2017) standards, referring to the ventilation filter requirements, test the filtration efficiency of ventilation filters at the minimum size of 0.3 micrometers. These two recent standards assume that this particle size corresponds to the Most Particle Penetration Size (MPPS) of mechanical filters. However, studies on mechanical media have shown that MPPS could shift to smaller particles when operational conditions change (in particular filtration velocity) and when the medium’s characteristics vary (as the fiber diameter). The literature then mentions rather a size range from 100 nanometers to 300 nanometers. One laboratory test bench dedicated to the filtration performance of ventilation filters allowed to obtain experimental data as a function of NaCl particles from 20 nm to 500 nm and according to different conditions. Another laboratory setup has been used to measure the classical media filtration used in the three filters tested. The results show that MPPS is still observable experimentally, and greater than 100 nm. Measurements are consistent with filtration modelling and allow to complete their information on the filters’ MPPS. Indeed, the results show that the range of 150 – 500 nm is a better MPPS estimation, unlike the fixed diameter of 300 nm, in the conditions used in this study.