The Effective Filtration

Efficiency of a Face Mask

Considerations and discussion (reflection)

Face masks, whatever the type of mask we are talking about, have become our companions on our daily trips in 2021. They are even more important than house keys or mobile phones due to the fact that we are obliged to wear them. In the last months people in scientific, political or social forums have discussed about the suitability of one or other type of face mask. This suitability analysis has been always carried out based on “theoretical” parameters about Bacterial Filtration Efficacy and Breathability (differential pressure). We want to emphasize that this analysis has been done based on theoretical data.

Due to the fact that the use of face masks to protect ourselves from Covid-19 has caught us all unprepared and without an specific knowledge about face masks, we believe that it is essential to debate about the Effective Bacterial Filtration Efficiency of any face mask based in reality and not in supposedly true dogmatisms or apriorisms, so that we invite you to calmly analyze what types of face masks are the best ones to really protect us.

Therefore, at this point, the big question when we put on and use a mask is: Is its Effective Filtration Efficiency for the Human Being the same as its “Theoretical” Filtration Efficiency? The answer is NO.


It is obvious and important to remark that there is a Human Being that Needs to Breathe behind a face maskand not an object to be protected (for instance a stone), and that if a face mask significantly prevents or ostensibly hinders the passage of air through it (it does not go out the flame or does not practically move blowing through it with some pressure greater that the one we use when breathing) that mask can hardly protect us in relation of B.F.E when we breathe, as we will not breath through the face mask, but through the holes that are formed in its perimeter adjustment. These holes are usually the holes in the cheek and the hole that is between the nose and the eye socket and the air that comes out through this last hole make glasses fog up.

When we were observing people in the Street wearing face masks with different facial adjustments in June 2020, we wondered about the Effective Bacterial Filtration Efficiency of a face mask in relation to its “Theoretical” Filtration Efficiency (the one which is measured in laboratories). This is mainly a physics problem and we carry out the study that we attach and that we present for your consideration, to relate the Effective Filtration Efficiency of a face mask to its “Theoretical” Efficiency.

There are two fundamental parameters that define the Efficiency Coefficient “on this study (KE), and those are Breathability and Facial Adjustment ( values expressed ​​in percentages).

Therefore, we notice that the Effective Bacterial Filtration Efficiency depends on Breathability and Facial Adjustment, and as the Human Being needs breathe to live, if breathability of each fabric, that it is fixed due to the characteristics of the fabric makes air difficult to pass through, then the Facial Adjustment, which is less rigid and more flexible, will gradually give way to be able to breathe through the perimeter holes, that is, not through the face mask. We remember that breathing involves making a minimum pressure and therefore much less than the pressure of blowing.

We consider that it is relevant to generate an open debate how we should design and manufacture face masks in the future to protect us in normal situations (although hopefully we hope that we do not need to use them) and we consider that the main characteristics for a Face mask talking about the Effective Filtration Efficiency should be:

  • An Optimal Breathability (minimum Pa / cm2) so that we could breathe through them.
  • Good Facial Adjustment (Design and Twistband).
  • High Bacterial Filtration Efficiency (the one measured by laboratories) got it through hidrofuge treatment, antibacterial treatments and also applying Nanotechnology.

Although we are discussing about the Effective Filtration Efficiency, it does not hurt as a complementary factor, to analyze the consequences of the use of the different face masks for the Environmental Sustainability.