(1) Thermal insulation: Any material which significantly slows down or retards the flow or transfer of heat. Building insulation types are classified according to form (e.g loose-fill, batt, flexible, rigid, reflective, and foamed-in-place) or material (mineral fiber, organic fiber, foam plastic). All types are rated according to their ability to resist heat flow (R-Value or RSI).

(2) Electrical insulation: A non-conductive wire covering, often rubber, thermoplastic, or asbestos. The thickness of insulation varies with wire size and type of material, application or other code limitations.