Hygroscopic means that a material attracts and absorbs water vapour from the air and releases that moisture again when the air becomes drier. A material settles at an equilibrium moisture content that matches the relative humidity.
Characteristics
Many building materials are hygroscopic, such as:
- Wood
- Loam
- Lime
- Gypsum
- Brick
- Cellulose
Salts are also strongly hygroscopic.
Benefit
Hygroscopic materials buffer moisture and thus help to regulate the indoor climate: they absorb moisture at high humidity and release it again at low humidity.
Risk
- Salts in masonry attract moisture and can effloresce.
- Hygroscopic moisture can keep a wall damp.
Related terms
- Relative humidity
- Equilibrium moisture content
- Vapour transport
- Loam
- Capillary
- Condensation
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