Door Panel Padding; 1/8" Closed cell foam
Here's the foam I use when I assemble a complete set of Forever Panels.
It's closed cell, 1/8" thick.
The factory used a 1/4" open cell that was very light. You can crush it flat with a finger. This foam is a nice upgrade to make the door panels feel a bit more modern, but not look out of place. Assembled with this foam, the door panel is about the same thickness as stock, but looks clean and taught, not pillow-like.
In the photos, I have traced the outline of the door panel in the photos above just to show how 2 door panels fit on the slice of foam. The traced outline will not be there on the set you receive - just trace your Forever Panel with a sharpie. Also, the foam you get may not be 1 large sheet, it may be 2 sheets (cut in half lengthwise). This will be done to get it within first-class postage regulations - it won't affect your door panel building at all.
*there are extra photos above showing what the foam looks like under the vinyl. All of the above door panels are 1) Forever Panels, 2) 1/8" closed cell foam, 3) high quality automotive vinyl; all assembled with DAP Weldwood Landau top adhesive.