pass through window use?

Years ago, when we were young and didn't have a care we let people ride in the truck camper.

We had an inflatable airbag, I don't know what else to call it, that went between the truck and camper. Stopped wind rain etc.

We would pass food through and on occasion the skinny of us would trade spots, truck back seat and camper, LOL

Now we know better, I am not sure what you would use it for. Heat transfer maybe? Or air conditioning.