An insulator is a material that does not allow electricity or heat to pass through it. ASBESTOS and dielectric are two materials commonly used as insulators. ASBESTOS is an 8-letter word and is a naturally occurring mineral that has been used in insulation for centuries. Dielectric is a 10-letter word and is a synthetic material that is often used in electrical insulation. Both materials are effective at preventing the flow of electricity and heat, making them ideal for use as insulators.