Freez-Kontr’l HD is a heavy-duty 70% propylene glycol-based heat transfer fluid formulated for hydronic applications where its multi-component inhibitor formulation provides added robustness for better service life. The specially developed formulation achieves a higher maximum operating temperature of 325 deg F, higher reserved alkalinity, better thermal stability and added stability when mixed with water containing up to 350ppm total hardness in closed loop applications. Freez-Kontr’l HD is a pink colored solution to aid in system leak detection.