This page refers to thermal insulation. For electrical insulation see insulators, and for sound insulation see sound proofing. Often the same techniques used for thermal insulation can be used for sound insulation as well.
Insulation is sometimes confused with either weatherization or thermal mass, but is distinct from both.
Insulation is the practice of providing a barrier surrounding, or within a building or other object to slow the conductive flow of heat. A reflective barrier is often added to insulation to slow radiative heat flow.
Insulation is a barrier keeping in heat flow.
Insulation is used not only for buildings, but also for stoves, refrigerators, freezers, water heaters and some other appliances where it is important to slow heat flow, and in many industrial applications.
Commonly-used types of insulation in residential construction include:
The use of highly-compressed straw bales as insulation, though uncommon, is gaining popularity in experimental building projects and passive solar design because of its high R-value and excellent thermal mass.
A vapour barrier is often used in conjunction with insulation because the thermal gradient produced by the insulation may result in condensation which may damage the insulation. The vapour barrier should always go on the warm side of the insulation. That is, on a heated house, the vapour barrier goes between the warm inside and the insulation. On an insulated, air conditioned house in very warm climates, the vapour barrier should go on the outside so that the insulation is between the vapour barrier and colder, air conditioned house.