Mostly, these materials make effective heat sinks through their ability to store large amounts of heat at relatively low temperatures.
Cooling systems take advantage of this. The coolant in a car's engine can absorb much larger quantities of heat than can the iron (or aluminum) engine block. This makes it a very effective means of conveying heat away from the engine.
Large bodies of water store vast quantities of heat, even though the temperature of the water remains below ambient (outdoor) temperature through mot of the summer. This heat is released in autumn (or even through the winter if you live in an area that does not experience a freeze-over), and is very effective in keeping the seasonal temperatures moderate.