Mercedes M class, 2001. Was gifted this car with only 110,000 miles on it! But the vents keep shooting out this mess pictured. Face and defrost. Probably feet too. Appears to be some kind of foam substance. What is it? Should I be concerned?
Thank you!
The various control doors in the vent system have foam applied to them so they don’t make noise when these doors change position.
What you’re seeing is this foam coming off the doors and blowing out the vents.
Tester
I suspect it is some sort of foam used at the various joints in the HVAC system. Me? I wouldn’t worry about it, though you may develope some rattles. But, I could be wrong.
The foam inside your evaporator housing is disintegrating and blowing in your face
nothing to be concerned about
just be glad the vehicle was free, because these vehicles were considered gravy trains for mechanics working at Benz dealers and independent shops specializing in that brand 
that money you didn’t have to spend buying the vehicle should be set aside for future big 
repairs
Foam it is. I had that with a used pickup truck and while annoying it is harmless and will stop eventually. I would wrap masking tape with the sticky side out around a popsicle stick and pull loose pieces out once in a while.
18+ y.o. Merc.
Just be glad bits of “stuff” aren’t dropping onto the road as you drive.
