Thermal energy is widely used to generate electric power. In order to reduce the thermalenergy losses, thermal insulations are widely used. The performance of the thermal insulationmaterial is measured by its thermal conductivity, which is dependent on the operating conditionssuch as compression, temperature, and air gaps. In this work, two commonly used insulationsin thermal power plants, namely, glass wool and rock wool are investigated. At first the thermalconductivity of both the materials are measured using sophisticated Transient Plane Source (TPS)technology. Since the TPS equipment is expensive, a heat flow meter based on 1-D heat conductionis fabricated and the results are compared with TPS. Next, thermal conductivity as a function ofcompression is measured using TPS and compared with results obtained from fabricated test set up.The variation in in thermal conductivity with compression is also numerically modeled. The modeltakes input from TPS experimental data and predicts thermal conductivity at different compressionratios with good agreement. Lastly, the changes in effective thermal conductivity due to improperthermal insulation with air gaps are investigated using infrared (IR) imaging equipment. Annularand eccentric air gaps in thermal insulation are created and investigated. The study is useful inestimation of the thermal performance of insulation materials and will be helpful for engineers inpower plant and building industry