What is this part and what does it do?
 

This is random I know.
Have a 96 XJ sport, got it a few months ago and have been restoring it...previous owner took care of it in regards to oil changes but that about it. So doing a restore project and currently spray painting fender flares, roof rack, etc.
So I opened all 4 doors and removed the plastic kick plates, cleaned them up, painted then and such.
Now hopefully you guys can follow me..sorry no pics. On my Cherokee when you open the rear doors there are 2 plastic vents that go into opening in the wheel wells I guess you can say. I pulled them off and the were caked up with dirt and grime. Cleaned them up...looks like inside these vents are foam inserts that seem to act as filters I guess.
Pretty knowledgable about auto mechanics but I am baffled as to what these are and what they do? Is there any reason I should find a way to replace these foam inserts?
Like I said random I know..just wondering if anyone has any answers?

Those vents relieve air pressure. When you drive with your windows closed

Gotcha, learned something new. Thanks bud.

I burned those in the bonfire

Are you suggesting that the engineers believed a Cherokee would be so well sealed when the windows were rolled up that some form of supplementary ventilation was required to prevent... uh, suffocation? Well, it works really well to vacuum out all of the gas and exhaust fumes that inevitably get into the cab through the 1/2 inch panel gaps and ill-fitting seals.

The engineers were pretty optimistic.

I thought i read somewhere they were also for preventing window blowouts when shutting the doors, so the rush of air has somewhere to go. No idea if that is true or not.

All possible suggestions...just wondering about those foam inserts if it is to filter out fumes and such. Should I try to replace them or just let it be? They were solid caked up with lint, dirt, etc. Just wondering cause this is my daily driver that my 2.5 year old daughter will be riding in.

Use some light compressed air. Maybe rinse it out with soap and water. It's not a cabin filter so your kids will be fine. I wheel my Jeep all the time and have my son With me all the time. Mine are the same way.