The P2 disposable masks increase inhalation resistance. The longer they are used, the more difficult it is to breathe due to absorbed dusts. Furthermore, their effectiveness is reduced accordingly to the growth of carbon dioxide and water vapour between the half-mask bowl and face (so-called dead zone). The carbon dioxide concentration within the dead zone increases after every exhalation.
Therefore, P2 disposable respirators with non-return exhalation valves, accelerating gas circulations, are recommended in order to improve the comfort of use and improve effectiveness of the mask. The valve allows carbon dioxide to escape, which makes the mask safer and more comfortable to wear.