The foam insulation is a couple layers. There are two foam layers, with the foil backing facing both the outside and the inside. I’ll describe it here:
1. Exterior Sheet metal
2. Small air gap where possible (approximately 1-2 mm)
3. 2″ polystyrene foam
a. foil backing
b. 2″polystyrene
c. poly plastic substrate
4. Mylar hvac tape on foam block seams
a. There are 1×3 furring strips at 24″ intervals the length of the bus to hold the foam in place and provide a solid backing for attaching the final interior wall and other items (lights, walls, cabinets etc). A single self tap screw holds the wood to each metal rib. The screw is the cold bridge between the steel exterior and interior.
b. 0.125″ thick acrylic foam tape placed over each screw head to mitigate thermal conduction.
5. 0.75″ polystyrene foam
a. poly plastic substrate
b. 0.75″ polystyrene foam
c. foil backing
6. Mylar hvac tape on foam block seams
7. ABS sheet panels (this is the final interior permanently affixed)
8. Wallpaper, fabric, or other decorative coverings.
I forgot to add that a number of areas where I was lazy or didn’t get the foam cut quite right, I filled cracks with the red can “great stuff” spray foam. I probably burned through about 10-15 cans of the stuff. It was on sale for like 2 bucks a can when I got it so it’s not like I put a lot of money into dow’s bank.