From wikipedia:
The design of the surgical masks depends on the mode; usually, the masks are three-ply (three layers). This three-ply material is made up of a
melt-blown polymer, most commonly polypropylene, placed between
non-woven fabric.
[32] The melt-blown material acts as the filter that stops
microbes from entering or exiting the mask.
[32] Pleats are commonly used to allow the user to expand the mask such that it covers the area from the nose to the chin. The masks are secured to the head with ear loops, head ties, or elastic straps.
[33]
Physical properties of surgical masks Parameter Typical unit Pressure differential, ∆P cm of H2O / cm2 Filtration and exposure % Liquid penetration resistance
mbar Air permeability ml/s⋅cm2 at 100
Pa Water vapor permeability g/24 hr⋅cm2 Water repellency grade Filter material in the middle layer may be made of
microfibers with an electrostatic charge; that is, the fibers are
electrets. An electret filter increases the chances that smaller particles will veer and hit a fiber, rather than going straight through (electrostatic capture).
[34][35][36][
better source needed][
medical citation needed] While there is some development work on making electret filtering materials that can stand being washed and reused,
[37] current commercially produced electret filters are ruined by many forms of disinfection, including washing with soap and water or alcohol, which destroys the electric charge.
[38] During the COVID-19 pandemic, public health authorities issued guidelines on
how to save, disinfect and reuse electret-filter masks without damaging the filtration efficiency.
[39][38] Standard disposible surgical masks are not designed to be washed.
