Can house wrap block moisture?
At present, the minimum pass-through preventable by the house wrap is 0.02 micron. Water vapor is made up of water vapor molecules. The molecular diameter of water vapor is about 0.0004 micron. So the house wrap can not prevent water vapor from passing through.
The working principle of house wrap is that the water particles are very small in the state of water vapor. According to the principle of capillary movement, the water particles can penetrate the capillary to the other side smoothly, thus the phenomenon of steam permeability occurs. When the water vapor condenses into water droplets, the particles become larger. Because of the surface tension of the water droplets (the water molecules "pull and balance" each other), the water molecules can not smoothly break away from the water droplets to penetrate into the other side, that is, to prevent the water from penetrating, so that the house wrap has waterproof function.