The mask is a medical device that helps cover the mouth and nose, it serves as a barrier to minimize the transmission of infectious agents between people. So, before choosing the correct mask or face mask, you should know the difference between particle filtration efficiency and bacterial filtration efficiency, these terms refer to the permeability capacity of the mask, where:

• Particle filtration: These are tests where aerosol particles are used and they serve to identify if your mask retains the passage of inert particles such as dust, droplets, etc. If your mask meets this parameter, the packaging must declare its PFE (particle filtration efficiency) value as a percentage.
• Bacterial Filtration: It is a permeability test where the passage of microorganisms is analyzed, in the case of surgical masks they must have a bacterial filtration value of 95% or higher, and you can see this on the box of your mask with the acronym BFE (bacterial filtration efficiency).

Now, which of these 2 filtration modalities protects me against Covid? Both, we are going to relate the bacterial efficiency with the virus, the Covid has a measurement between 0.09 to 0.13 microns and a bactera measures between 0.2 to 1 micrometers in diameter, the virus needs to adhere to a larger agent in order to migrate. In this case, it adheres to saliva droplets, which is why masks with BFE > 95% are the most recommended to use. 

Next, we share with you a study carried out by the University of Cambridge, with the different mask fabrics testing with Bacteriophage MS2 Particles (5 times smaller than the coronavirus) where the following results were obtained:

Also, the University of Cambridge suggested that the adjustment of this implement is equal to and even more important than the material from which it is made. So, try to make your mask cover your nose and mouth. First adjust the nose clip and then stretch the lower part to your chin.
Lastly, check that there is no space between your cheeks and the mask, in case there is any space left, adjust the elastics.

Note: during this process avoid touching the inside of the mask.