Insulating for Heat

Most recent answer: 10/22/2007

Q:
Whish insulator do you think is best; bubble wrap, tin foil or black paper and why? (these insulators are for warming a cup of tea, can I please have a very scientific explanation)
- nida khan
Walthamstow School For Girls, London
A:
Nida -

There are 4 big ways that heat can travel: convection, conduction, radiation, and evaporation. Let’s think about these one at a time.

Convection:
This happens when air moves around. It picks up heat in one place and moves it to another. In order to prevent this from happening, you want to keep your cup of tea somewhere where the air is very still, so no heat can get away. Perhaps you may want to put a lid on it.

Radiation:
This is heat that radiates off of something. For example, if you put your hand near (but not touching!) a hot stove, it will feel warm there. This is energy being radiated straight off of the stove and onto your hand. To prevent this, you want the surfaces near the tea to be the sort that don’t absorb much heat. For example, a white surface will absorb much less heat than a black one. (Think of riding in a white car vs. a black one when it’s really hot outside.) A shiny surface will absorb even less, since it reflects heat back where it came from.

Evaporation:
This is when water evaporates and carries heat away. This can be especially important with a hot liquid like tea, since the steam can carry a lot of heat. In order to prevent heat from escaping like this, you will want to keep the container closed and water-proof, so the moisture can’t get out.

Conduction:
Last but not least. This is what happens when something hot physically touches something cold. Heat moves from the hot surface into the cold one, warming it up. To keep this from happening, you should use a material that heat can’t move through very easily. But how do you know what sort of a material that is? Try some experiments. Wrap up a hot cup of tea in each of the insulators that you’re thinking about. Set your hand on the outside of the insulator and see how hot it feels. The hotter it feels on the outside, the more heat is escaping from the inside.

I think from here you should be able to figure out exactly what material (or materials) to use on your own. Good luck!

-Tamara

(published on 10/22/2007)