Impact of Humidity Cycles on the Long-term Thermal Conductivity of Mineral Wool Insulation

The heat resistance of mineral wool insulation is important because buildings are energy efficient. Environmental factors usually undermine the long-term stability of such materials, especially when they are exposed to changing humidity conditions. In this research, the effects of repeated humidity cycles on the thermal conductivity of mineral wool insulation were tested under representative conditions of real-life exposure. Controlled wetting and drying periods were applied to standard mineral wool samples, and careful thermal analysis was carried out via the guarded hot plate technique. Further characterization was carried out via terminational monitoring (TGA) and scanning electron microscopy (SEM) to analyze the change in mass and to determine the structural changes that occur over time. The results revealed an irreversible and systematic increase in the thermal conductivity with increasing number of humidity cycles. The thermal conductivity increased by approximately 45% after ten full cycles compared with when it was dry. This loss is attributed to moisture being trapped, thickening of the fiber structure and collapse of the internal pore spaces, which act to increase conductive heat transfer. SEM analysis revealed that the significantly compacted and microstructurally distorted samples were also reflected in the cycled samples. After full drying, the thermal conductivity did not recover to its initial value, which underlines the long-term effect of cyclic changes in humidity. This observation indicates that when rating the suitability of insulation material for building applications, long-term involvement with the environment must be considered. To preserve the thermal performance, the study suggests the use of hydrophobic treatment or protective vapor barriers. The approach and lessons given can guide future benchmarks and material testing procedures, increasing the robustness and energy consumption of building designs in fluctuating climate environments.