If it’s like other masks I’ve seen there is a flap or rubber gasket in there that acts as a one way valve. The US military uses M-50s and that’s how they work too
It’s normally closed. When you breathe in the air is drawn through the mask filter. When you breathe out the pressure pushes the flap open. When your exhale stops there isn’t enough pressure to keep it open and the flap seals up again.
If it’s like other masks I’ve seen there is a flap or rubber gasket in there that acts as a one way valve. The US military uses M-50s and that’s how they work too
It’s normally closed. When you breathe in the air is drawn through the mask filter. When you breathe out the pressure pushes the flap open. When your exhale stops there isn’t enough pressure to keep it open and the flap seals up again.