From your work and your knowledge, you already know that materials are chosen for their properties.

However, some materials have special properties which make them useful for keeping things warm or cool.

Did you know that heat travels from a warm place to a cool place?

Here, the heat energy travels from the hot coffee, through the ceramic cup, and from the cup to our hands and also the air surrounding it.

Some materials allow heat to travel through them quickly and easily - these are called thermal conductors.

Materials that slow down the movement of heat energy are called thermal insulators.

Now, it isn't only heat that can be conducted. Did you know that metals have a special property: they conduct electricity, which means that they allow electricity to pass through them easily. They are called electrical conductors.

Metal wires make up the circuit in the toaster. But we don't get an electric shock each time we use the toaster!

This is because other materials don't conduct electricity. These are called electrical insulators and they are used to cover the metal parts of the toaster.

Did you notice that the same words - conductor and insulator - are used both for conducting heat and electricity? Just go back and read those sections again.

Right, with all that in mind, let's have a closer look at solids.