When preparing a van for ply and carpet lining, you will hear two terms constantly: Sound Deadening and Thermal Insulation. While people often confuse them, they serve two completely different purposes.
What is Sound Deadening? A bare metal van is essentially a large drum. When driving, the road vibrations make the large metal panels shake, creating a loud, echoing boom inside the cabin. Sound deadening mats (usually made of butyl rubber and foil) add mass to the metal. You stick them directly to the van walls and seat them using a roller, stopping the vibration and killing the road noise. It makes your van quiet, but it does not keep you warm.
What is Thermal Insulation? Thermal insulation (like fleece, closed cell foam) stops the transfer of heat. It keeps the cold winter air out, breaks the cold bridge and traps the heat inside (or vice versa in summer). Insulation is installed over the sound deadening and behind your ply and carpet lining.
The Verdict If you are just using the van for work purposes, a simple ply lining might be enough. But if you spend hours driving or plan to sleep in the van, you need both sound deadening (for quiet) and insulation (for comfort) before installing your wood panels.