In filtering facepiece respirators (FFRs) and elastomeric half mask respirators (EHMRs), exhalation valves typically include a membrane composed of natural rubber, silicone, or neoprene. This membrane sits atop a support structure and lies beneath a plastic cover.
Here is the mechanism of the Exhalation Valve & Inhalation valve. Valves on masks and respirators are very simple: plastic base, middle rubber and plastic cover; to make it simple, we will take away the top cover to see how the rubber and base work with the air. The middle silicone rubber is very soft, so you can move it by your breathing.
