The thermal conductivity or heat transfer rate of copper is 92% versus aluminum which is approximately 49%. However, the copper fin bonded to the tubes, or water passages, using lead solder is very inefficient and slows the heat transfer rate to just slightly better than that of aluminum. This can be a disadvantage of copper if the bonding process does not allow the copper fin to touch the brass tube, and why not all copper/brass cores of similar design, but different manufactures, transfer heat equally.
Copper/brass radiators, because of their weight and durability, have been around a long time and can be easily disassembled and reassembled for cleaning purposes. Not the case with aluminum, unless speaking of the O.E. version that comes with crimp mounted plastic tanks. As a result the life expectancy of the aftermarket aluminum radiators will be far less than that of copper/brass.
To better understand the function and performance of any given radiator it helps to understand the “cooling” process and think of it in a way that allows for comparison. The words cooling, or better cooling, or efficient cooling are thrown around a lot in advertising and promotional terms but for the most part un-quantifiable at best without a reference or yardstick to measure by.
To measure and control the cooling processes you have to take several variables into consideration. Variables include engine temperature production at different rpm’s, or engine operating btu output, coolant absorption rates, coolant flow rates, or gpm’s, and coolant temperature reduction rates that will vary with the size of the radiator and the amount of (cfm’s), speed, and temperature of the air flowing through the radiator. The only device to actually compare one radiator vs. another with absolute control is to have a wind-tunnel that can duplicate actual driving conditions under various specified conditions. U.S. Radiator built radiator dyno or test stand in 1999 and tested every core design and manufacturer, in both copper/brass and aluminum, for plain and simple temperature drop, inlet to outlet, at specific and controlled parameters.