Contrary to popular belief, N95 masks do not strain the air that people breathe. Filtration in N95 type masks is based on particles sticking to mask fibers. They have four mechanisms to ensure that unwanted particles do not pass through. The first, inertial impaction, is where large particles collect on fibers due to possessing insufficient inertia to stay in the flow of the air. The second is interception, it occurs when the airflow brings the particle in contact with the fiber and it sticks. The first two mechanisms collect large particles. The third is diffusion, this is specific to smaller particles. Essentially, very small particles will diffuse around randomly until they come into contact with the fiber. The final and most important mechanism is electrostatic attraction. In electrostatic attraction, charged particles are attracted to the charges on the fiber, which is critical because it works regardless of the particle’s size. In particular, electrostatic attraction is very effective against mid-sized particles, which typically have the deepest penetration. This aspect is so important that mask performance is calculated using particles of this size, which is about 0.3 μm. Large and small particles range from 0.05μm - 0.05 μm respectively. N95 masks accomplish these mechanisms using several layers of nonwoven materials. The filtration aspect of a mask is the most clearly necessary, however the most important consideration is the mask’s fit; if it is able to be worn without leaks.

Despite their functionality, N95 masks are made with polyester and polypropylene, both of which are petroleum derived materials known to contribute to microplastic pollution in the environment. N95 masks become less effective as the charged layer loses its charge; and the main cause of this loss of charge is humidity.