Foam makes for a full, rich appearance.....good example was rolled and tucked vehicle seats back in the '60's. A 2" roll of foam (or other who knows what material) under vinyl, making an arched/rolled surface and a stitched seam, etc, etc, etc. Take expensive chairs like in high dollar offices where you have a puffy seating/back surface, with capped pins attached to the chair frame at regular intervals across the surface, making the surface puffy and rich looking. I'm doing a 1/20th scale 1848 US Western Stagecoach which has such puffy upholstery.....just starting to do that part....we'll see how it goes.
On my Starcraft Holiday restoration I didn't use any as it was a fishing boat and I made it look like one. The vinyl was stretched directly over acrylic coated marine plywood.
