eddie jr

Any idea what the purpose of the thin black foam on the surface of the temperature and air diversion flaps/doors is (in the heater box)?? I was cleaning out the ducts and the box and noticed it was in rough shape and gooey......so I ended up scraping it off since I didn't want that falling off and getting in the airstream. Is there a good reason it is there? It doesn't appear to be for sealing since it covers the entire flap as opposed to just the edges. And if you touch it, it never bounces back, it just stays squished.

thanks.