Since the filters cannot be cleaned and reused and have a limited lifespan, cost and disposability are key factors.

[3] Mechanical filters remove contaminants from air in the following ways:[4][5] More obscure mechanisms include: Considering only particulates carried on an air stream and a fiber mesh filter, diffusion predominates below the 0.1 μm diameter particle size.

[11] The fibers are charged as they are blown to produce an electret,[12] and then layered to form a nonwoven polypropylene fabric.

[9][10] Filtering facepiece respirators consist mainly of the mechanical filtration medium itself, and are discarded when they become unusable due to damage, dirt, or excessive breathing resistance.

When tested according to the protocol established by NIOSH each filter classification must demonstrate the minimum efficiency level indicated below.

For R type filters, a 200 mg of DOP is used, with a defined service time of "one work shift".

European standard EN 143 defines the 'P' classes of particle filters that can be attached to a face mask.

[30] Respirator standards around the world loosely fall into the two camps of US- and EU-like grades.

According to 3M, respirators made according to the following standards are equivalent to US N95 or European FFP2 respirators "for filtering non-oil-based particles such as those resulting from wildfires, PM 2.5 air pollution, volcanic eruptions, or bioaerosols (e.g. viruses)":[33] The NPPTL has also published a guideline for using non-NIOSH masks instead of the N95 in the COVID-19 response.

[58] Fit and comfort do not seem to be harmed by UVGI, moist heat incubation, and microwave-generated steam.

This has been seen in attempts to sterilize by soaking in soap and water, heating dry to 160 °C (320 °F), and treating with 70% isopropyl alcohol, and hydrogen peroxide gas plasma[58] (made under a vacuum with radio waves[62]).

UVGI (ultraviolet light), boiling water vapour, and dry oven heating do not seem to reduce the filter efficiency, and these methods successfully decontaminate masks.

[63] Gamma radiation and high energy electrons penetrate deeply into the material and can be used to sterilize large batches of masks within a short time period.