When using glycol/water mixtures it is important to consider how cold the fluid will get, but it is also equally important to consider how the fluid will be used at that temperature. Will the fluid be stagnant or will it be circulated? Is the glycol for winterization? These questions ultimately affect the mixture ratio of the glycol. For example if a coolant loop or system is being winterized and temperatures will fall down to -10°F at the lowest, a mixture of 30% propylene glycol to 70% water will be enough to protect the system. 30% propylene glycol has a freeze point of 8°F but the burst point is -18°F. This system will be protected but the coolant will be slushy. By definition, freeze point is the temperature where ice crystals begin to form. The fluid will become slushy but will not expand. The burst point of a fluid is the temperature where the fluid will freeze solid, expand, and break pipes or damage other parts of the equipment.