This study investigates the potential for enhancing the thermal performance of external walls insulation in warmer climates through the combination of phase change materials (PCMs) and bio-based materials, specifically hemp wool and wood wool. Experimental tests using the heat flow method (HFM), and numerical simulations with ANSYS Fluent software were conducted to assess the dynamic thermal distribution and fluid-mechanical aspects of phase change materials (PCMs) within composite walls. The results demonstrate a notable reduction in peak indoor temperatures, achieving a 58% reduction with hemp wool with a close 40% reduction with wood wool when combined with PCMs. Fluid-mechanical analysis indicates that PCMs act as efficient indoor temperature regulators by storing excess heat during hot periods and releasing it later during phase transitions. Furthermore, the homogeneous distribution of the liquid fraction and natural convection during phase change contribute significantly to the improvement in heat transfer rates, resulting in a 96% reduction compared to hemp wool and wood wool without PCMs.