Why do some cups keep ice colder than others?

At first, every ice cube started out the same.

But after sitting in different cups, some began melting much faster than others.

The reason isn't that one cup is somehow making the ice colder. The difference is how quickly thermal energy can travel through the material.

Heat naturally moves from warmer places to cooler places. Because the air, table and cup are warmer than the ice, thermal energy moves towards the ice.

As the ice gains thermal energy, it begins to melt.

Why does the cup material matter?

Different materials allow thermal energy to move through them at different rates.

Materials that allow heat to move through them easily are called conductors. Metals are usually good conductors, so thermal energy can travel through them relatively quickly.

Materials that slow down heat transfer are called insulators.

Paper, cardboard, foam and even trapped air can act as insulators because they make it harder for thermal energy to reach the ice.

A good insulator doesn't actually make the ice colder.

It simply helps the ice stay cold for longer by slowing down heat transfer.

What did your investigation test?

During your investigation, you changed the material surrounding the ice while trying to keep everything else the same.

The ice cubes started at a similar size.

They were tested for the same amount of time.

The main thing you changed was the material.

That made it a fair test.

By comparing how much each ice cube melted, you weren't just watching ice disappear — you were collecting evidence about which materials slowed heat transfer most effectively.

Scientists and engineers use exactly this kind of evidence when choosing materials for real products.

Curiosity Spark

Insulation is everywhere.

It helps keep drinks cold in an esky, keeps food warm in a thermos, slows heat entering our homes, and even helps protect spacecraft and astronauts from extreme temperatures.

Sometimes engineers even combine several different materials or trap pockets of air to make better insulation.

If you had to design the ultimate container for keeping an ice cube frozen...

Which materials would you choose — and how could you prove your design works?

Try These Next

Ice Balloon Challenge – Investigate what happens when water freezes inside a balloon.

Cloud in a Jar – Explore how temperature changes can help form tiny water droplets.

Water Balloon Timebomb .  – Discover how water can protect a balloon from the heat of a flame.