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7. Hygroscopic and non-hygroscopic materials
A hygroscopic material has the property of binding a certain quantity of moisture contained in the air or liquid water (in contact with it).
The experimental fact that highlights this phenomenon is the variation in its mass when placed in the presence of moisture.
untreated glass wool is hygroscopic, whereas polystyrene and polyurethane are not.
The water vapour permeability of non-hygroscopic materials is unaffected by ambient conditions: the same permeability coefficient is found by dry cup and wet cup calculations.
This is not the case for hygroscopic materials. For the latter, water vapour permeability increases with the relative humidity of the environment: slowly for relative humidities...
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Hygroscopic and non-hygroscopic materials
Multi-layer walls
