Thermal Conductors & Insulators

You may have noticed that when you touch different objects in the same room, some feel warmer and others feel cooler. Metals tend to feel cooler and other materials, like wood or the carpet, feel warmer (or the same temperature as your hand).

Many people think that this is because they are at different temperatures. But they are actually the same temperatures: the temperature of the room they are in, usually about 72°F or 22°C. The reason that some materials feel warmer and other materials feel cooler has to do with the type of materials they are: whether they are thermal conductors or thermal insulators.

Particles (atoms/molecules) that make up metals and other thermal conductors more easily speed up or slow down (remember, atoms and molecules are always moving around at temperatures found on the earth). On the other hand, particles that make up thermal insulators are more resistant to changing speeds when they come in contact with objects at different temperatures.

Thermal conductors. Some materials, including metals, are "thermal conductors." These materials are good at transferring thermal energy. When you touch thermal conductors that are at room temperature (72°F or 22°C), thermal energy is transferred from your hand (which is at your body temperature, about 98°F or 36.7°C) to the material. Because your hand loses thermal energy (that is, the particles that make up the surface of your hand lose some of their speed), it feels cooler.

Thermal conductors such as metals are also good at converting sunlight (solar radiation) to thermal energy (molecular motion). This is why when you touch a metal object that has been sitting outside in the sun, it feels very hot. It feels hotter than objects that are not thermal conductors (like the grass or a picnic blanket).

Thermal insulators. Other materials, like cotton, which is used to make many clothes, are "thermal insulators." These materials are not good at transferring thermal energy. So, when you touch these materials, little or no thermal energy is transferred from your hand to that material. Because your hand does not lose much thermal energy, these insulators feel like they are about the same temperature as your hand.

This is one reason why cotton and most clothing materials are thermal insulators. If they were not insulators, you would probably feel very cold most of the time because your body would keep losing thermal energy!

Insulating materials like glass, plastic, and Styrofoam are often used for drinking cups. This is because they keep cold drinks cold and hot drinks hot.

The table below shows examples of materials that are better insulators and materials that are better conductors of thermal energy:

Examples of Thermal Insulators and Thermal Conductors

Insulators	Conductors
Rubber/Latex	Silver (Ag)
Glass	Copper (Cu)
Wood	Aluminum (Al) Foil
Cotton	Iron (Fe)
Plastic	Water (H_₂O)
Styrofoam	Gold (Au)

(Click here for Periodic Table.)

Check your understanding...

(Click here for Periodic Table.)

Q1: What is the main reason that some materials are better thermal conductors than other materials?

a) They have crystal-like structures.

b) Their particles (atoms & molecules) absorb energy.

c) Their particles (atoms & molecules) change speeds more easily.

That's correct! The particles of materials that are good thermal conductors more easily speed up (or slow down) when they come in contact with hotter/cooler objects or other energy sources (like light). So, (c) is the correct answer.

Actually, the particles of materials that are good thermal conductors more easily speed up (or slow down) when they come in contact with hotter/cooler objects or other energy sources (like light). So, (c) is the correct answer.

Q2: For your science experiment, you put a block made of aluminum and an identical-sized block of wood in the sun for 10 minutes. You then measure their temperatures (using an infared thermometer). Which of the following will be true?

a) The wood block will be warmer.

b) The aluminum block will be warmer.

c) They will be the same temperature!

d) I don't know.

That's correct! Aluminum is a better thermal conductor than wood. This means that light from the sun will more easily cause aluminum atoms to move around faster compared to atoms of wood. So the temperature of the aluminum block will increase faster than the temperature of the wood block. (So, (b) is the correct answer.)

Well, aluminum is a better thermal conductor than wood. This means that light from the sun will more easily cause aluminum atoms to move around faster compared to atoms of wood. So the temperature of the aluminum block will increase faster than the temperature of the wood block. (So, (b) is the correct answer.)

Q3: You promised your friend that you would bring ice cream to her birthday party on a warm sunny day. You bought two one-pint containers of vanilla chocolate chip ice cream (her favorite). You wrap one container in aluminum foil, and the other in the same amount of plastic wrap. Your mom drives you to your friend's house (30 minutes away) while you hold both ice cream containers in your hands. Which of the following is most likely true:

a) More ice cream wrapped in aluminum foil will be melted.

b) More ice cream wrapped in plastic wrap will be melted.

c) The ice cream will be melted the same amount in both containers.

d) I really don't know.

e) Other.

You're right! More of the ice cream that is wrapped in aluminum foil will have melted. This is because more thermal energy from your hand (which is at about 98°F or 37°C) will be transferred to the ice cream during the trip. As a result, the ice cream wrapped in aluminum foil will melt more. So, (a) is the correct answer.

Well actually, more of the ice cream that is wrapped in aluminum foil will have melted. This is because more thermal energy from your hand (which is at about 98°F or 37°C) will be transferred to the ice cream during the trip. As a result, the ice cream wrapped in aluminum foil will melt more. So, (a) is the correct answer.