The ideal option is polystyrene foam or mineral slabs due to its resistance and durability. The distance between the outer and inner plane of the door should accurately calculate. As a rule, this is 4 or 5 cm. It is not difficult to calculate the thickness, it is enough to measure the thickness of the door leaf and deduct the thickness of the skin on both sides. Do not forget about the size of the door length. If desired, you can replace the internal casing.
