RE: HVAC air filter? or interior filtering issue?
I've been pulling bits of foam from my vents for quite some time now.
I think the foam is used as gaskets in the HVAC case and ducts.
I'm not going to worry about it unless I have to pull the instrument panel for something else, like a heater core replacement.
I wish companies would stop using cheap foam that deteriorates in 10 years. I've seen many instances of this, especially in the surrounds of expensive speakers.