Coolant is a valuable resource drawn from sap of the rare Ice flower, which only grows in areas of extreme cold.
Ice flower sap is highly volatile in its natural form, making it very dangerous to harvest. In addition to possibly exploding when exposed to air, the sap is also likely to quickly freeze harvesters in their tracks.
Only relatively recently were Engineers and Arcanists able to develop a method to safely stabilize the sap. The resulting coolant has many uses, from preserving food to curing heat stroke; while it's not strictly vital for survival, it does make life in Bastion a little easier.
