Thermal radiation is one of the four ways by which heat moves through a structure. Thermal radiation is electromagnetic radiation emitted from the surface of an object, due to the object's temperature. Infrared radiation from a household radiator or electric heater, or the light emitted from a typical incandescent light bulb, are common examples of thermal radiation. Thermal radiation is one of the four ways heat moves through a structure. (See also air infiltration, convection and conduction)

R-Value is a measure of a material's thermal conduction (see conduction). Unfortunately, R-Value has taken hold in the consumer's mind as a universal method for comparing insulations - the higher the R-Value, the better the insulation, which is not the case. R-Values are not measure only one of the factors that determine how an insulation product will perform in the real world.

Insulation is, first and foremost, meant to stop the movement of heat. The problem with using R-Value as the sole yardstick of an insulation's effectiveness is that heat moves in and out of your home or office in four ways: by conduction (which R-Value measures), and by convection, radiation and air infiltration (none of which R-Value measures) (see FAQ question on R-Value).

Retrofitting refers to the process of installing insulation in a finished, presumably older, structure. The process involves, typically, removing a band of exterior siding for each story, drilling holes to allow access to stud bays, installing dense-packed cellulose insulation, sealing the holes and replacing the siding.