1. Introduction

Medical masks usually consist of two outer layers of non-woven material, an inner filter layer, a nasal retainer, and elastic ear loops. The outer layers are used to protect against the penetration of large particles. The inner layer is the most important filter layer that holds both large particles and smaller particles, in particular micro-organisms. Also, the inner layer has a certain hygroscopicity for absorbing large particles of water vapor, which may contain microorganisms.

The main filter layer is usually a non-woven material obtained in the process of spinning polypropylene microfibres. Microscopic fibers of this material perform both mechanical and electrostatic filtration. As a result of the electrostatic effect, small dust particles and water droplets containing various bacteria and viruses are absorbed by the surface of the material and do not pass through it. This material can provide filtration in accordance with different standards: BFE95 (95%), BFE99 (99%), VFE95 (99%), PFE95 (99%), KN90 (90%). Usually, flat medical masks use meltblown with a density of 20-25 g/m2. A denser material provides better filtration (for example, N95 masks use meltblown with a density of 40 g / m2), but makes it more difficult to breathe.