Conductor or insulator?

Is It a Conductor or an Insulator?

  • Grades 3-8
  • 15 minute activity
  • NGSS 5-PS1-3

Quick answer

Metals are conductors, so coins, keys, foil, paper clips and spoons all let electricity through. Plastic, rubber, glass, wood, paper and air are insulators, so they block it. Things that are wet or salty, like salt water, pickles and your skin, conduct a little. Below are 32 everyday objects and what happens when you test each one with a play dough circuit.

Chart of 32 everyday objects sorted into conductors, insulators and objects that depend, as tested with a dough circuit
Tap to enlarge. Green: the LED lights, so the object is a conductor. Red: the LED stays dark, so it is an insulator. Orange: it depends.

The quick rule

Ask one question: is it made of metal? Metals have electrons that can move freely from atom to atom, so electricity flows through them easily. Almost everything else in your house, like plastic, rubber, wood, glass, paper and cloth, holds its electrons tightly, so it blocks electricity.

The tricky cases are things that are wet or salty. Pure water barely conducts, but water with salt or minerals dissolved in it does. That is why salty play dough conducts and sugar dough does not. Learn the science in Conductors and Insulators.

Conductors: the LED lights

  • Paper clip: yes, a conductor. It is made of steel.
  • Coins: yes. Pennies, nickels, dimes and quarters are all metal, so all of them conduct.
  • Aluminum foil: yes. Foil is a thin sheet of metal and a very good conductor.
  • Keys: yes, they are metal.
  • Metal spoon or fork: yes. A plastic spoon does not.
  • Steel nail or screw: yes.
  • Safety pin: yes.
  • Scissors: the metal blades conduct. The plastic handles do not.
  • Bare copper wire: yes. Copper is used in almost all real wiring because it conducts so well.
  • Metal ring or chain: yes. Gold, silver and steel all conduct.
  • Pencil lead: yes. The "lead" is really graphite, a form of carbon that conducts.
  • Colored Squishy dough: yes. The salt in it lets electricity flow.

Insulators: the LED stays dark

  • Plastic pen, straw or LEGO brick: no. Plastic is one of the best insulators, which is why wires are coated in it.
  • Rubber band, eraser or balloon: no. Rubber is an insulator.
  • Craft stick or other dry wood: no.
  • Paper or cardboard: no, as long as it is dry.
  • Glass marble: no. Glass is an insulator.
  • Crayon: no. Wax is an insulator.
  • Cork: no.
  • Felt or cloth: no, as long as it is dry.
  • Dry leaf: no.
  • White Squishy dough: no. It is made with sugar instead of salt, so it insulates.
  • Air: no. Air is an insulator, which is why a small gap between two pieces of dough stops the LED.

It depends

  • Water: pure water is a poor conductor. Tap water conducts a little because of the minerals in it, and salt water conducts well. Try a cup of plain water, then stir in a spoonful of salt.
  • Your hand: your body does conduct electricity, because it is full of salty water. Dry skin resists so much that 6 volts cannot push enough through to light the LED. That is why wall outlets, with far more voltage, are dangerous.
  • Lemon or pickle: sour and salty juice conducts a little. The LED may stay dark or glow very faintly. A pickle usually does better than a lemon because it is so salty.
  • Soda can: the can is aluminum, but it is covered in paint and a thin plastic lining, which insulate. Touch the shiny metal on the top rim or the bottom and it conducts.
  • Wooden pencil: the wood insulates, but the graphite core conducts. Sharpen both ends and touch the lead to the dough.
  • Wet wood or paper: the water soaked into them conducts a little, especially if it has salt in it.

Try it with dough

Test your own objects

Make a conductor tester from play dough and an LED, then test anything you can find. Predict first, then test.

You need

  • Battery holder with 4 AA batteries
  • Conductive (salty) play dough
  • 1 LED
  • Objects to test from around the house or classroom

Steps

  1. Make three pieces of conductive dough and line them up with a small gap between each piece.
  2. Push the red battery wire into the first piece and the black wire into the third piece.
  3. Put the LED across the first gap: long leg in the first piece, short leg in the middle piece.
  4. Switch the battery holder on. The LED stays dark, because the second gap breaks the loop.
  5. Write down your prediction, then press an object across the second gap so it touches both pieces of dough.
  6. If the LED lights, the object is a conductor. If it stays dark, it is an insulator. Record your result.
Diagram of a dough conductor tester: a paper clip across the gap lights the LED, a plastic pen keeps it dark
A paper clip completes the loop and the LED lights. A plastic pen blocks it and the LED stays dark.

What happens

Every metal object lights the LED. Plastic, rubber, glass, wood, paper and air keep it dark. Salty and wet things are in between.

Not working?

Nothing lights, even with a paper clip? Push the middle and last pieces of dough together for a second. If the LED still does not light, flip it around and check the batteries. A faint glow means the object conducts a little: it has a high resistance.

Key words

Conductor
A material that lets electricity flow through it easily, like metal.
Insulator
A material that blocks electricity, like plastic, rubber or glass.
Metal
Materials like copper, steel, aluminum, gold and silver. All metals conduct.
Graphite
A form of carbon used in pencil lead. Unlike most non-metals, it conducts.
Prediction
What you think will happen before you test it.

For teachers

This sorting activity supports NGSS 5-PS1-3: make observations and measurements to identify materials based on their properties, including electrical conductivity. Have students build a three-column table (object, prediction, result), then sort their results by material and look for the pattern: every metal conducts.

The "it depends" objects make good discussion starters. Why does salt water conduct when pure water barely does? Why can your body conduct but not light the LED? (The 6 volt battery cannot push enough current through dry skin.) Older students can measure the difference with a multimeter in our Resistivity Lab. Find more lessons on our education page.

Conductor or insulator questions

Is a coin a conductor or an insulator?

A coin is a conductor. Pennies, nickels, dimes and quarters are all made of metal, so electricity flows through them and the LED in a dough tester lights up.

Is aluminum foil a conductor?

Yes. Aluminum foil is a thin sheet of metal and a very good conductor. You can even use a strip of foil in place of a wire in a dough circuit.

Is water a conductor or an insulator?

Pure water is a poor conductor. Tap water conducts a little because of the minerals dissolved in it, and salt water conducts well. Because most water has something dissolved in it, never mix water and wall electricity.

Is wood a conductor or an insulator?

Dry wood is an insulator. Wet wood conducts a little because of the water inside it.

Is rubber a conductor?

No. Rubber is an insulator, which is why it is used for gloves, boots and coatings that protect people from electricity.

Is pencil lead a conductor?

Yes. Pencil "lead" is really graphite, a form of carbon that conducts electricity. It has more resistance than metal, so the LED may glow a little less brightly.

Is the human body a conductor?

Yes. Your body is mostly salty water, so it conducts. Dry skin has a lot of resistance, so a 6 volt battery holder cannot push enough electricity through you to light an LED, and you will not feel it. Wall outlets have much higher voltage, which is why they are dangerous.

Is glass a conductor?

No. Glass is an insulator. It is used on power lines to hold the wires without letting electricity escape.

Next, try a project

Build the Conductor Project A free step-by-step conductor tester project with printable instructions.

Keep learning