As a material science expert, I can tell you that the ability of a material to conduct electricity is determined by the presence of free electrons within its structure. Free electrons are those that are not tightly bound to any particular atom and can move freely throughout the material, allowing an electric current to flow.

Rubber, being a polymer, is generally considered an insulator. This is because it lacks free electrons that can move easily through the material. The long chains of molecules in rubber are covalently bonded, meaning that the electrons are shared between atoms in a way that does not allow them to move freely. This lack of free electrons is what makes rubber a poor conductor of electricity.

However, it is important to note that the term "insulator" is relative. While rubber is a very good insulator under normal conditions, it can become conductive under certain circumstances. For example, if rubber is doped with certain materials or if it is subjected to high temperatures, it may gain some conductivity. But this is not typical for rubber as we commonly understand it.

Additionally, it's worth mentioning the concept of semiconductors. Semiconductors, unlike insulators, have a moderate number of free electrons. Their electrical conductivity can be significantly altered by introducing impurities into the material (a process known as doping) or by changing the temperature. This property makes semiconductors extremely useful in electronic devices, where their conductivity can be precisely controlled.

To summarize, rubber is an insulator and does not conduct electricity under normal conditions due to the absence of free electrons. It is one of the materials that we rely on to prevent the flow of electricity in many applications, such as electrical insulation and protective gear. However, the behavior of materials can be complex, and there are always exceptions and special cases to consider.

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If a material lacks these free electrons (also called conducting electrons)--as rubber does--it will not conduct electricity and is called an insulator. There are also in-between materials, called semi-conductors, which behave as a conductor or insulator, depending on the amount of voltage applied to the material.read more >>