Adhesive Pads on Ceiling

Sound deadening. The pads reduce resonance.

My van has three on the ceiling and two on each rear wall. They appear to be asphalt based pads which I think is what the original Dynamat products where made from. The front doors also have small triangle shaped pads that are butyl instead of asphalt and aren't much bigger than a Dorito chip. Butyl caulk or tape is also what's used to secure the plastic dust shields inside the doors.

The pads work on the premise that securing to even a small area on a body panel can greatly reduce the resonance which makes the vehicle quieter. You can test the effect yourself by tapping on a panel without the pad and then tapping on a panel that includes one.

The Sprinter vans I've seen use a lot more and basically have a pad stuck to every section of the roof.