Comparative Experimental Analysis of Wet-State Thermal Performance in Pipe Mineral Wool Insulation with Different Hydrophobic Treatments

Pipeline insulation is critical for energy-efficient building heating systems, as moisture ingress significantly degrades thermal performance and increases energy losses. This study experimentally evaluated how quality characteristics of mineral wool affect the thermal performance of pipe insulations (wired mats) at temperatures ranging from 20 °C to 85 °C with moisture content up to 12% by weight. Thermal conductivity measurements were performed on two representative samples using the “guarded hot pipe” and direct water injections. Thermal conductivity measurements confirmed the expected increase with rising temperature and moisture content for both samples. In a dry state, quality parameters have practically no effect on the thermal conductivity (0.036–0.041 W∙m−1·K−1). In a low-temperature regime, the inferior quality sample (Sample A) at a maximum moisture content of 12% exhibited thermal conductivity of 0.042 W∙m−1·K−1, and the sample with the best hydrophobic treatment (Sample B) had a thermal conductivity of 0.050 W∙m−1·K−1. At an elevated temperature at a moisture content of 12%, Sample A and Sample B had thermal conductivity of 0.077 W∙m−1·K−1, and 0.109 W∙m−1·K−1, respectively. The results suggest that highly hydrophobic materials are advantageous only in high-temperature applications where rapid moisture removal occurs after short-term ingress, providing critical data for optimizing insulation selection and improving energy conservation in heating networks.