when you upgrade the interior you can add a thint layer of rubberization, betwixt the metal and the door cards or other interior lining fabric or decorative plastic applied there, to absorb the sound, for the sound deadening. Just make sure it's thickness will soften the ņutside and inside sounds to your hearing satisfaction. See, the reason that foil is adequate for holding in the insulation and refracturing the sunlight also serves another purpose. The 't' in thint is the outer layer of foil, sort of like a sun shade? Stands for made from tin. Protect us from the other, it will!