Thermal insulation is a material that blocks or slows the flow of heat through the building envelope. Insulation is vital to most green building design because it allows spaces to retain what heat they have, while avoid gaining excess heat from outside.
Materials used for insulation fall into two broad categories:
(1) Fibrous or cellular products – These resist conduction and can be either inorganic (such as glass, rock wool, slag wool, perlite, or vermiculite) or organic ( such as cotton, synthetic fibers, cork, foamed rubber, or polystyrene).
(2) Metallic or metalized organic reflective membranes – These block radiation heat transfer and must face an air space to be effective.
http://sustainabilityworkshop.autodesk.com/buildings/insulation
