Aluminum (Al): Great Conductor and Great Insulator. How Can This Be?

The other day, I was boiling corn on the cob for a family cookout using my old college workhorse pot. Its durability and effectiveness is attributed to one thing: Aluminum. Aluminum is a very strong and ductile material that also has a low heat capacity (Cth). Uh….professor, what does that mean? Simple: This pot is rough and tough and when you put it contact with a flame, it is going to heat up—fast!

That same day, I was up it my attic gathering some old family photo albums. The temperature outside was 85°, a little warm for this time of year. Yet, I was relatively comfortable rummaging through the attic. The secret: Aluminum. I have installed an aluminum radiant barrier in my attic. Aluminum has an extremely low level of emissivity (e). Uh…professor, you’re losing me, please explain? Simple: The aluminum foil is reflecting the outside heat, thereby insulating the attic!

So if I use aluminum to cook with, because it heats up fast, why would I dare use it to insulate with? After all, isn’t the point of insulation to NOT allow things to heat up fast?

The answer lies in the fact that heat is transferred in three separate mechanisms: conduction, convection, and radiation. My tasty corn on the cob is quickly warmed because the flame from the stove is in direct contact with the aluminum: A great conductor for conduction of heat. My attic is cool because the radiant heat from the outside is reflected by the aluminum: A great insulator for radiation of heat.