1, this problem is mainly depending on the contract you signed with the above 2, there is no clear guideline, if the owners is rich, you can coat moisture-proof layer containing sackcloth material and two layers of 25mm thick plaster protective layers on the 70mm bulk fiber heat conservation layer outside the air duct, and coat the outer edge with two layers of aluminium paint.
Aluminum foil layer itself is a protective layer, which has no need to be increased more protective layers, is using glass cloth for heat conservation layer, you can buy glass fiber cloth without aluminum foil protective layer. However, the protective layer of aluminum foil is really easy to damage, but its impact on air duct is not larger than water pipe, which is acceptable.
