Vapour barriers made of cardboard or paper usually consist of 2 - 3 layers of construction cardboard or kraft paper, which are glued together. In some cases, parafin layers are incorporated for better fire resistance and glass fibers for higher tear resistance. Especially with vapour barriers made of cardboard or paper, it is important to pay attention to whether they have an approval for blow-in insulation, as a certain tear resistance is required for this. Vapour barriers should only be used in the case of a vapour-permeable roof structure, with underlays with an sd value ≤ 0.5 m, which allows controlled moisture transport from the inside to the outside.
Source: bauwion
