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Vapour diffusion resistance (µ)

The vapour diffusion resistance is an indicator of how far water vapour is hindered in diffusing within a material.

An insulation material with a low µ value is called vapour permeable. In a vapour permeable structure water that has penetrated the insulation material can easily escape.

Especially insulation materials made from natural fibres have low vapour diffusion resistance and thus very good diffusion properties.