Abstract: Harsh environment conditions are challenging for thermal management of electronics devices due to the thermal load from the surroundings. Phase Change Material (PCM) based Passive Thermal Management Systems (PTMSs) are gaining more attention for electronics cooling, and thermal insulation protection is crucial in hot air environments. In this work, an experimental setup was developed to study the thermal response of a PCM based PTMS under the thermal protection of different insulation when exposed to a hot air environment. Stearyl Alcohol was used as the PCM for PTMS. The effect of Vacuum Insulation Panel (VIP) integration in PTMS under a heat flux range of 0.3 to 1.4 kW/m2 was analysed and compared with the performance of a commercial Cellulose Fibre Insulation (CFI). Effect of thermal insulation thermal protection and thermal energy storage capability of PCM on the thermal response of the PTMS was investigated separately in different configurational settings. PTMS integrated with VIP having thermal conductivity of 6.2 mW/m-K showed better performance in Set-Point Temperature analysis. The results confirmed the synergic effect of VIP integration and PCM on extending the Safe Operational Time (SOT) of the PTMS. PCM based PTMS with VIP showed a 41.63 % average improvement in SOT. Duration for complete phase transition of PCM was improved to 46.34 % through VIP integration over different heat generation rates. VIP outperformed CFI on improving SOT by offering better thermal resistance against thermal load from hot air environment, thereby proving its potential application in PTMS under a hot air environment.