You are probably more familiar with conductors than you realize. If you have ever poured a cup of tea, worn an oven mitt, or taken a sip from a thermos, you already have some firsthand experience with thermal conductors.
Heat likes to travel, but only in one direction. Did you know heat travels only from warm or hot things to colder things? This makes sense when you realize there is no such thing as “cold." There is only heat. Cold is simply the absence of heat!
If you hold an ice cube in your bare hand, it might seem like the coldness of the ice cube makes your hand cold. The truth, though, is that your hand is actually warming up the ice cube, as heat travels from your warm body to the cold ice.
Then there are materials called "insulators" that do not allow energy to pass through easily. These materials include plastic, cork, wood, Styrofoam, and rubber. Thermal insulators are thus good at maintaining a consistent level of heat — whether hot or cold.
As you may have guessed by now, insulators make poor conductors. Manufacturers use this scientific fact to make products we use safer.
The body of the teapot must be able to conduct heat in order for the water inside to boil. Since metal is a great conductor, it easily passes heat from the stove to the water inside. That's why manufacturers use metal for the body of the teapot.
You already know it would be a very bad idea to touch the body of the teapot with your bare hand. Thankfully, it has a handle. If the handle of the teapot was metal, however, it would also conduct heat from the stove — to your hand — and that would be a very unpleasant surprise.
In order to prevent burns, manufacturers make handles out of good insulators, such as wood and plastic. This means you can enjoy a warm drink without burning your hand.