Reflective insulation differs from other insulating materials in the manner in which it retards heat transfer. Unlike the other Insulating Products, Reflective Insulation works by reflecting incident infrared radiation, thus reducing radiant heat transfer. Reflective insulation is fabricated from aluminum foil with backings applied to provide a series of closed air spaces. Its insulating value is derived from the heat-reflective surfaces separated by air spaces into which the radiation is reflected.
The key to maintaining a comfortable temperature in a building is to reduce the heat transfer out of the building in the winter and reduce heat transfer into the building in the summer.
Heat is transmitted across confined air spaces by radiation, convection, and conduction. Different types of insulation products reduce heat transferred by radiation, convection, and conduction to varying degrees. As a result, each provides different thermal performance and corresponding "R" Values (resistance to heat flow). The "R" value can depend on the heat flow direction. With reflective insulation the greatest "R" values are achieved when reducing downward heat flow.
The primary function of reflective insulation is to reduce radiant heat transfer across open spaces, which is a significant contributor to heat gain in summer and heat loss in winter. The low emittance metal foil (usually aluminum) surface of the product blocks up to 97% of the radiation and therefore blocks a significant part of the heat transfer.
Reflective Insulation Systems are fabricated from aluminum foils with a variety of backings such as kraft paper, plastic film, polyethylene bubbles, or cardboard. If a single reflective surface is used alone and faces an open space, such as an attic, it is called a radiant barrier. Radiant barriers are sometimes used in buildings to reduce summer heat gain and winter heat loss. Some studies have show that it can be more effective in keeping heat out of homes in hot climates than keeping heat in homes in cold ones.
Heat flow by radiation has been brought to the public's attention with high efficiency windows, which commonly use the term "Low E" to advertise the higher performance ratings. This value is measured in emittance or "E" values ranging from 0 to 1 (lower "E" value indicates better performance). Most building materials, including fiberglass, foam and cellulose have "E" values in excess of 0.70. Reflective insulation typically has "E" values of 0.03 (again, the lower the better). Therefore, reflective insulation is superior to other types of insulating materials in reducing heat flow by radiation. All radiant barriers must have a low emittance (0.1 or less) and high reflectance (0.9 or more). The term reflective, in reflective insulation, is in some ways a misnomer because aluminum either works by reflecting heat (reflectance of 0.97) or by not radiating heat (emittance of 0.03). Whether stated as reflectivity or emittance, the performance (heat transfer) is the same. Like other insulation, reflective insulation is labeled with R-values, which provide a measure of thermal performance.
Reflective insulation differs from conventional mass insulation in the following:
Materials, Applications and Advantages of Reflective Insulation
Reflective insulation has been used effectively for decades and is available throughout the world. The following are the major types of reflective insulation currently available:
Some common applications are:
Other advantages are: