Here's why:

* Electrons are tightly bound: The electrons in rubber are tightly bound to the atoms, making it difficult for them to move freely. This means that electricity cannot flow easily through rubber.

* High resistance: Rubber has a very high electrical resistance. This means that it opposes the flow of electricity.

* Used in electrical applications: This insulating property is why rubber is widely used in electrical applications like electrical wires, cables, and protective gloves.

However, there are some exceptions:

* Conductive rubber: There are specialized types of rubber that are made conductive by adding carbon black or other conductive materials. These conductive rubbers are used in applications like anti-static mats and grounding straps.

* Vulcanized rubber: Vulcanized rubber, which is used in tires and other durable rubber products, can become slightly more conductive over time due to the presence of impurities and aging.

So, while rubber is generally considered an insulator, its conductivity can vary depending on the type and its specific application.