Have you ever opened a Thermos bottle, and wondered at its ability to keep hot things hot, and cold things cold? How can something as simple as a mirrored glass flask inside a tin container have such temperature sustaining attributes? The answer is really quite simple: The Thermos relies on the principle of radiant barriers, or reflective insulation.
The principle was first documented by Sir James DeWar around 1872, when he learned that a reflective surface inside a vacuum could vastly improve the ability to keep hot things hot and cold things cold. His DeWar flask became the forerunner of both the Thermos bottle and such highly technical things as NASA's space suits. This same principle can be applied to keeping our homes warm in the winter, in the form of radiant barriers.
How Radiant Barriers Work to Block Heat Transfer
There are three distinct types of heat transfer - conductive, conducive, and radiation. Conduction is the ability of heat to transfer through a medium, and is accomplished by the movement of heat on air currents. Ordinary insulation in a home primarily works both to stop heat loss and to maintain the integrity of an air conditioned space. Insulation is generally manufactured of fiberglass in newer installations, and keeps the home warmer or cooler through conduction; because fiberglass is a poor conductor, less heat is lost from the home.
Convection, on the other hand, is the ability of a gas or liquid to transfer heat from one level to another. As a surface is warmed, it replaces the air in the upper level with warmth, and the produced heat then circulates to the cooler levels to begin the process once more. Think of your furnace - it forces warm air through its system into your home, and the resulting warm air rises, then cools and is returned to the system through the cold air registers in your home to begin the cycle again.
The third type of heat transfer is radiation. Heat, just like light, travels by radiation. Think once again of the Thermos bottle. Its interior walls are composed of a glass or stainless steel material that is highly reflective. The reflection of the heat from the hot coffee keeps the interior of the Thermos hot for a long period of time. It is not dependent on the movement of air (a product of conduction), or the heating of a gas or liquid (as produced by convection).
Radiant Barriers in Residential Insulation
Radiant heat barriers have been around for many years. In the 1940s and 50s, many forward thinking home builders were realizing that to seal out cold in a home during the winter, and to keep cool air in the home in the summer, a combination of dead air spaces and aluminum foils could be utilized to accomplish these results. The inventor Dr. Alexander Schwartz introduced in 1945 an invention he called "INFRA," and many architects and builders of that time readily embraced this solution as a means of solving insulation issues.
By the early 1960s, millions of square feet of this type of reflective barrier were installed in homes around the United States. Then the untimely death of Dr. Schwartz left his company without a leader. The FTC also made a ruling that crippled his distribution methods, and the company closed its doors in 1965, thus effectively taking his product off the market.
In later years, many companies begin to reproduce this discovery , and now there are many manufacturers that produce and sell reflective radiant heat barriers. Several methods are used. One manufacturer uses "bubble wrap" covered on both sides with aluminum. The bubbles in the wrap provide the "dead air" space needed for radiant heat barriers to work properly. It is then used on water heaters, water pipes, and ductwork because of its ease of installation and its ability to provide both the dead air space and reflective qualities needed to work properly. Other manufacturers laminate the aluminum foil to cardboard, fiberglass, foam, and other traditional building materials. These laminates are used in new home construction and retrofits.
Continue to Part 2: Installing Radiant Barrier Insulation >
Alden Smith is an award winning author and regular contributor to DoItYourself.com. He writes on a variety of subjects, and excels in research.