The variation of thermal conductivity of fibrous insulation materials under different levels of moisture content

Thermal insulation plays an important role in determining the thermal and energy performance of a building. The effectiveness of thermal insulation is dependent on its thermal conductivity (k-value) and its ability to maintain its thermal characteristics over an extended period of time. However, the k-value can be greatly reduced by the presence of moisture within the insulation materials. For example, when circumstances are conducive, under hot–humid climatic conditions, condensation may occur within the insulation material, raising its moisture content well above the hygroscopic level. The objective of this paper is to investigate experimentally the impact of moisture content on the thermal conductivity of commonly used fibrous insulation materials. Three types of material with different densities are investigated with the emphasis on fiberglass. A comparison of the behavior and magnitude of k-value changes according to moisture content levels indicated appreciable variations. Higher thermal conductivity at a given operating temperature for the investigated densities is always associated with higher moisture content. The relationship between k-value and moisture content is found to be affected by the initial conditioning moisture content level. Materials having similar density but conditioned at different initial moisture content levels exhibit different relationships between k-value and moisture content. The rate of change in thermal conductivity with moisture content is higher at higher initial moisture content. The results should be of great importance to material manufacturers, building owners and designers when selecting suitable insulating materials and correctly predicting the thermal and energy performance of buildings and their energy-efficiency.