[Pontirag]

hope this is clearer

as for the expandibel foam. its a really really bad idea. many who tried it in aluminium skinned aircraft found that , at first it adhered to the innder skin of the aircraft but over time vibrations would cause a separation between the foam and the skin. condensation would collect between foam and the skin and very quickly rot the skin from the inside out. it would no doubt do the same to a cars sheet metal.