When making ice in the freezer for coolers always seems weird to add a bunch of salt to water but actually makes the cooler stay cold longer. 🧊
Water when it freezes can’t get any colder. Ice in pure water is never colder then about 30 degrees. Add salt and you can reduce the freezing point to 20 or 25 degrees so the ice is colder. Colder ice keeps the cooler colder and therefore the cooler lasts longer.
Same principle of why they use salt in ice cream. Not just flavor but also to make ice cream extra cold.