If a material is not effective at conducting electricity, it is called what?

A material that is not effective at conducting electricity is referred to as an insulator. Insulators are designed to prevent the flow of electric current, thereby providing a barrier that protects against electrical shock and limits the loss of energy. Common examples of insulators include rubber, glass, and certain types of plastics.

In contrast to insulators, conductors are materials that easily allow the flow of electricity, such as copper and aluminum. Resistors, while they resist the flow of current, are still conductive materials, just with higher resistance, and semiconductors fall somewhere between conductors and insulators, with conductivity that can be altered by the introduction of impurities or through changes in temperature. Thus, the primary characteristic that defines an insulator is its ineffectiveness in conducting electricity, making it crucial for applications requiring electrical safety and efficiency.