dampmotstand

Dampmotstand, or moisture resistance, is a property of a material or a layer that describes how strongly it resists the diffusion of water vapor. It is a key parameter in the study of moisture transport in building envelopes, textiles, and packaging, where controlling vapor flow helps prevent condensation, mold growth, and material damage.

The moisture resistance of a material is commonly quantified by the diffusion resistance factor, denoted as μ. This dimensionless value compares the material’s resistance to water vapor diffusion with that of plain air (μ = 1). In practice, designers also use the Sd-value, which expresses the material’s diffusion resistance as an equivalent thickness of an air layer: Sd = μ × d, where d is the material thickness (in meters) and Sd is measured in meters. Higher μ or Sd values indicate greater resistance to vapor diffusion and lower vapor permeability.

Measurement and standards for dampmotstand are defined in hygrothermal and building physics standards, such as those governing vapor diffusion in building components. Determination methods may involve standardized tests that simulate steady-state diffusion or cup-permeability techniques, and results are used to assess suitability for vapor barriers, insulation assemblies, and exterior or interior wall constructions.

Applications and implications: dampmotstand informs the design of moisture management strategies in buildings. Materials with high dampmotstand are effective vapor barriers, protecting sensitive layers from condensation, while low-dampmotstand materials allow moisture to diffuse more readily, aiding in drying and reducing moisture buildup under certain conditions.

Limitations: dampmotstand can vary with temperature, relative humidity, and material moisture content. It is not a fixed property and should be considered as part of an overall hygrothermal performance assessment. See also vapor barrier, vapor permeability, and Sd-value.