What to stuff van doors and empty space with?

[Trekking]

Any suggestions on what to fill the empty space with in the doors and in the back of the van with some more additional insulation. Will have to open empty spaces that can get stuff for something I would think.
Would fiberglass insulation work, Them from peanuts or just leave them open.

 

[Van-Tramp]

You can go to Home Depot or Lowe's and pick up some rigid insulation board. The higher the R-value, the greater it insulates. It is easily cut and glued into place.

http://www.homedepot.com/b/Building-Materials-Insulation-Rigid-Insulation/N-5yc1vZbaxx

 

[ZOFCHAK]

I insulated my Ford E-350 doors just using a roll of that fiberglass house insulation. I used the white stuff without the backing and just pulled sections off an jammed it into the body panels. Iknow that leaving it loose provides the higest R value, but I figured it was a tradeoff as leaving it loose would have also allowed it to settle over time. It was super easy and made a huge difference. The most noticeable change was the sound (No more tinny echo when you close the doors), but I'm sure it helps with the temperature as well. There are a lot of small, hard to get to areas, but with the fiberglass it was fairly easy to put it in most places.