The current is therefore constantly changing direction. Electricity flows more easily through some materials than through others. Conductors let electricity flow through them easily. Most metals are good conductors, so they are used to make wires for carrying electrical current. Insulators, such as glass, stop the flow of electricity.
Most plastics are insulators.
Wires carrying electricity are covered in plastic to prevent electric shocks. Resistance is the property of a substance that prevents the flow of electrons, and it is measured in units called ohms. Materials with high resistance, like Plexiglas and rubber, are called insulators, since they do not easily allow electricity to pass through them. Materials with low resistance, such as copper and aluminum are called conductors, because they let electricity flow through them easily. Electricity passing through a material will heat the material relative to the resistance of that material.