Heat Conductors and Insulators

Heat is always on the move

Have you noticed that a cup of hot chocolate slowly goes cold if you leave it, but an ice lolly slowly melts and goes warm? That is because heat is always moving. It never stays still.

There is one important rule to remember: heat always travels from a warmer place to a cooler place. Your warm hands give heat to a cold snowball. A hot radiator gives its heat to the cool air in the room. To learn more about the different ways heat moves, you can visit heat and how it travels.

But here is the interesting part — heat moves through some materials fast, and through other materials slowly. That is what conductors and insulators are all about.

What is a conductor?

A conductor is a material that lets heat pass through it easily and quickly.

The best heat conductors are metals — like iron, copper, steel and aluminium. If you hold one end of a metal spoon and put the other end in hot soup, the handle soon gets warm too. The heat travels quickly up the metal.

We use conductors when we want heat to move fast:

• A saucepan is made of metal so heat from the cooker passes quickly into the food.
• A radiator is metal so its heat spreads quickly into the room.
• A cooking ring carries heat straight to the pan.

What is an insulator?

An insulator is the opposite. It is a material that lets heat pass through slowly. Insulators block heat and slow it down.

Good insulators include wool, wood, plastic, rubber, fabric and even air. If you hold one end of a wooden spoon and put the other end in hot soup, the handle stays cool for a long time, because wood does not let the heat through quickly.

We use insulators when we want to stop heat moving:

• A wool jumper traps your body heat so you stay warm in winter.
• A saucepan handle is plastic or wood so it stays cool enough to hold.
• An oven glove protects your hand from a hot tray.
• A cool box keeps a picnic cold by slowing heat from getting in.

Why does metal feel cold?

Here is a puzzle. Touch a metal table leg and then touch a wooden chair in the same room. The metal feels colder, even though they are both the same temperature! Why?

The metal is not actually colder. Because metal is a good conductor, it quickly carries heat away from your warm hand. Your hand loses heat fast, so it feels cold.

The wood is an insulator, so it carries heat away from your hand slowly. Your hand keeps its warmth, so the wood feels warmer. The clever lesson here is that "cold" is really just your hand losing heat. Conductors take it away quickly; insulators let you keep it.

The secret of trapped air

Many warm things use a sneaky trick: they trap air. Still air is one of the best insulators of all.

Think about a fluffy wool jumper, a thick duvet, or a bird's feathers puffed up in the cold. They are full of tiny pockets of trapped air. That air does not let heat escape easily, so the warmth stays close to your body. This is also how double-glazed windows work — they have a layer of air (or special gas) trapped between two sheets of glass to keep heat inside the house.

Conductors and insulators all around us

Look around and you will spot them everywhere:

Object	Conductor part	Insulator part
Saucepan	Metal base	Plastic handle
Hot water bottle	(none)	Rubber + fluffy cover
Mug of tea	(none)	Pottery sides
Iron	Metal plate	Plastic grip

Engineers choose materials carefully so that heat goes exactly where it is wanted and is kept away from where it is not.

Try it yourself! 🧪

Which spoon stays coolest? Ask an adult to help, because this uses warm water.

You need a metal spoon, a wooden spoon, and a plastic spoon, plus a jug of warm (not boiling) water and a little butter or margarine.

1. Stick a tiny blob of butter near the top of the handle of each spoon.
2. Stand all three spoons in the jug of warm water at the same time, handles up.
3. Watch the butter. Which spoon's butter melts and slides first?

The butter on the metal spoon melts first, because metal is the best conductor and carries the heat up the fastest. The wooden and plastic spoons keep their butter solid much longer, because they are insulators that slow the heat down.

You have just proved which materials are conductors and which are insulators! Heat is a form of energy on the move — explore more in the many forms of energy.