Reflective insulation systems have only come into widespread use since World War II, and some of the more visible applications have been in high-tech projects like the space program. In the past few years, reflective materials have been increasingly used in construction and are rapidly gaining acceptance. Essentially they work on the same principle as an old-fashioned glass-lined thermos bottle, by reflecting "radiant energy."

Managing the temperature in a building always involves controlling heat transfer. Whenever there is a difference in temperature across a given area (for example, inside and outside a building), heat will move from hotter to colder regions until the temperature is the same across the whole area. The purpose of insulation is to impede this natural process. In hot weather, you want to stop heat from being transferred into the building, and in cold weather you want to stop it from being transferred out. Heat transfer occurs in three ways:

• Conduction -- the transfer of heat between two contacting surfaces. An example would be a steel pot being warmed on an electric range.


• Convection -- the transfer of heat by the flow of air or fluid. An example would be a room warmed by the hot air from the vent of a central heating unit.


• Radiation -- the transfer of heat by infrared radiation across an air space. An example would be the dashboard of a closed car heated by sunlight.

Traditional forms of mass insulation, like fiberglass, are effective in preventing heat transfer by conduction and convection, but they have virtually no effect on radiant heat (between 80 and 90% of the radiant heat striking fiberglass will pass through or be "emitted"). Radiant heat transfer typically has at least as much impact on the temperature in a building as do conduction and convection, and in many cases it is the most significant cause of unwanted heat loss or gain.

Aluminum foil, which can reflect up to 97% of the radiant energy that strikes it, has proven to be an outstanding component of reflective insulation systems. However, for a reflective surface to serve as insulation, there must be an air space between it and the area to be insulated. For example, if you wrap foil tightly around a potato and bake it in the oven, the foil will conduct heat to the potato and cook it. However, if you could somehow leave an air gap of an inch or so between the foil and the potato, the potato would never cook.

Reflective foil insulation is composed of two outer layers of aluminum foil with an inner layer of some inert material to create the required air gap between them. STEELBUILDING.COM now offers a reflective foil called Solarguard. Unlike most reflective foil products, which have a middle layer of polyethylene or some other plastic, Solarguard has ?" of fiberglass between the reflective outer layers, giving it some additional insulating power. We offer it in two configurations. Our "foil interior" insulation has 99% aluminum on both sides, but one of them is reinforced with a "scrim" of embedded fibers. The scrim side should be installed towards the interior where the insulation is more likely to receive stress. People who do not want the foil to be visible on the inside of their building can choose our "white interior" insulation, which has 99% aluminum foil on one side and a scrim-reinforced white facing on the other.

rFOIL™ Insulation Products can significantly reduce the overall heat transfer throughout your building when installed correctly. To create a superior, effective product, rFOIL™ uses various combinations of foil and polyethylene bubbles in their Single Bubble and Double Bubble series insulation. The aluminum layer reflects 97% of radiating heat waves to keep your building cool in the summer and warm in the winter. Polyethylene bubbles provide the necessary thermal break to eliminate condensation problems in metal buildings.

When compared to a mass insulation material like fiberglass, reflective foil offers some advantages. It is not affected by humidity or moisture, it does not lose its effectiveness when compressed, and it does not irritate the skin, nose, or eyes and requires no special handling or clothing to install.

The bottom line is that reflective insulation works. Based on our own personal experiences and reports from customers, we find it to be effective in both warm and cold weather, and we especially recommend it in hot climates for buildings that will not be air conditioned. Mass insulation can do little to keep a building from getting hot, but reflective insulation can make an otherwise unbearable environment a pleasant place to work.