When sourcing PCMs, the most critical factor is the Phase Change Temperature (Melting Point), which must align precisely with your application's thermal target. You must also evaluate the Latent Heat Capacity (kJ/kg); higher values indicate better energy storage efficiency. Additionally, verify the Thermal Conductivity to ensure the material can absorb or release heat at the required rate. For long-term reliability, request data on Thermal Cycling Stability, ensuring the material maintains its properties after thousands of freeze-thaw cycles.