Reflective building insulation has become a standard component of total insulation system design in both new construction and retrofits. Using reflective insulation for either home insulation or metal building insulation will increase the comfort level inside, protect against condensation and save on energy costs.

While other types of insulation are made to resist or impede the flow of warm air, reflective barrier insulation reflects back radiant (infra-red) energy from the sun so it does not penetrate the building. It can also reflect back radiant heat inside the house so it does not escape. The concept is simple: each unit of radiant heat energy that is reflected away from your home in summer and each unit reflected back inside during winter means less operation of your air conditioning and heating systems, less wear and tear on your equipment, and less money you pay in utility costs. That is why reflective foil is called energy insulation.

Reflective Insulations:

• Take Advantage of low thermal conductivity of air.
• Have enclosed air spaces with emmitance surfaces
• Have a mass insulation component in many cases (closed cell polyethylene foam for example).
• Aluminum foils of films have emmitances in the range of 0.03 to 0.05 (the lower the better).

The r-values of reflective insulations and mass insulation are based on the same fundamental equations.

Reflective insulation is commonly made of either aluminum foil attached to some sort of backing material. The better performing reflective insulations will have or two layers of aluminum foil surrounding closed cell polyethylene foam. Other products may have the aluminum foil surrounding bubbles or fiberglass. The aluminum foil component in reflective insulation will reduce radiant heat transfer by as much as 97%.

Reflective insulation is a commercial spinoff of the NASA Apollo Space Program. NASA used a reflective foil covering to create a radiant barrier for both the spacecraft and space suits to reflect the intense heat of the sun away from the astronauts by day and to reflect internal heat back inside the capsule or space suit at night for warmth. NASA estimates that "Using conventional insulation, a space suit would have required a 7-foot-thick protective layer." Reflective insulation brings this radiant barrier technology to consumers for all types of building applications.

Radiation is the transfer of heat (infra-red radiant energy) from a hot surface to a cold surface through air or a vacuum. Radiation is the dominant method of heat transfer in a building accounting for 65-85 percent of all heat transfer through walls, ceilings, attic and floors. Reflective insulation is an effective barrier against radiant heat transfer because it reflects back almost all of the infrared radiation striking its surface and emits very little of the heat conducted through it. Reflective insulation products also incorporate trapped air spaces as part of the system to retard the convective flow of heated air the way fiberglass insulation does. The total thermal performance of the reflective system varies with the size and number of enclosed reflective spaces within the building cavity.

The thermal resistance of insulation is measured in R-value, or resistance to the movement of heated air by convection. The higher the R-value the more effective the insulation will be in resisting convective heat transfer. R-value does not measure an insulation's ability to resist radiant heat. Mass insulation like fiberglass or foam board primarily slows convective heat transfer.

In contrast, reflective foil insulation facing an airspace like an attic, wall cavity, or crawlspace creates a radiant heat barrier. Aluminum foil reflects back 97% of radiant energy that strikes it. The generally accepted definition of a radiant barrier system specifies that the reflective material face an open air space. Radiant barriers that have no central layer of foam or bubbles to trap air are not insulation per se, and by definition, have no R-value. The idea is that a radiant barrier facing an enclosed air space (like an attic or a wall cavity) becomes a "reflective insulation" with a measurable R- value. Despite the advances in space technology in insulation systems based on understanding and modifying the effects of radiation, no universally accepted laboratory method has yet been devised to measure and report the resistance to heat flow of a multi-layer foil to properly compare reflective insulation to the R-values of mass insulation.

Reflective insulation is effective in floor systems above unheated basements and ventilated crawl spaces. Heat is lost through floors primarily by radiation (up to 93%). When reflective insulation is installed in the ground floors and crawl spaces of cold buildings, it prevents the indoor heat rays from penetrating down, reflecting the heat back into the building, thereby warming the floor. Since aluminum is non-permeable, it is unaffected by ground vapors. A properly installed reflective insulation system in the floor will act as a vapor barrier, significantly retarding penetration of ground moisture into the house above.

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• Light weight, very strong and easy to install
• Moisture-proof - will not allow moisture to pass through in either direction
• Eliminates condensation within the ceiling and walls when properly installed as a vapor barrier
• Unaffected by humidity with lower moisture transfer and absorption rates than mass insulation - no mildew, mold or fungus growth
• No significant mass to absorb and retain heat
• Very low emittance values "E-values" (typically 0.03 compared to 0.90 for most insulation) which significantly reduces heat transfer by radiation
• No change thermal performance over time due to compaction, disintegration or moisture absorption - common concerns with mass insulation
• Easier to install than fiberglass - can be stapled, nailed, glued or sewn
• Safer for workers to install than fiberglass - there are no fibers to breath or cause skin irritation, or eye irritation
• Nontoxic and non-carcinogenic - does not irritate the skin, eyes, or throat and contains no substances which will out-gas
• Carries a Class A / Class 1 Fire Rating
• Radon retarder - will limit radon penetration through the floor
• Not a nesting material for rodents, birds or insects
• Attractive in areas where the insulation shows such as in a metal building
• Reduces the "black globe effect" in animal confinement buildings
• Energy Savings - Research conducted by the Florida Solar Energy Center (FSEC) has shown that the installation of a radiant barrier can have significant economic benefits. Attics account for approximately 22 percent of the heat gain in a typical Florida house. Installing an attic radiant barrier will reduce heat gain through the roof by about 40 percent. This equates to a savings of 8 to 12 percent on the annual electricity costs for air conditioning in a typical Florida home. The summer peak energy use savings was as much as 27%. This study also showed that the average peak reduction from the radiant barrier system was three times a great as that produced by added insulation (a change from R-19 to R-13).

Reflective insulation (like other building products) carries certifications to ensure that it meets building code requirements. Look for insulation that is ICC-ES recognized and Energy Star Qualified.

ICC-ES is a nonprofit organization that does technical evaluations of building products, components, methods, and materials. ICC-ES evaluation reports provide evidence that products and systems meet code requirements. Their reports on code compliance are available free of charge to code officials, contractors, architects, engineers, and anyone else with an interest in the building and construction. Request a copy of ICC-ES reports at their website: www.icc-es.org/Evaluation_Reports/index.shtml.

ENERGY STAR is a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy designed to help people save money and protect the environment through rating energy efficient products and practices. Products that are rated by this program will be marked with an Energy Star.

There are many areas throughout a home to install reflective insulation. They include the attic, walls, floors, ceilings, roof, basement, garage and crawl space. Insulating these areas with reflective insulation can save you money and increase your living comfort.

To lessen heat flow by convection, a reflective insulation, with its multiple layers of aluminum and enclosed air space, is positioned in a building cavity (stud wall, furred-out masonry wall, floor joist, ceiling joist, etc.) to divide the larger cavity (3/4" furring, 2" x 4", 2" x 6", etc.) into smaller air spaces. These smaller trapped air spaces reduce convective heat flow. Reflective insulation can be used alone or combined with other types of insulation to complete the building insulation system.

Click here for comprehensive installation instructions using reflective insulation.

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NASA Scientific and Technical Information
HEATING AND COOLING EFFICIENCY FOR HOMES
http://www.sti.nasa.gov/tto/Spinoff2004/ch_6.html

Oak Ridge National Laboratory
Radiant Barrier Attic Fact Sheet
http://www.ornl.gov/sci/roofs+walls/radiant/index.html

Florida Solar Energy Center
Radiant barriers: a question and answer primer.
http://www.fsec.ucf.edu/en/publications/html/FSEC-EN-15/index.htm

Parker, D.S., J. R. Sherwin and M. T. Anello
FPC Residential Monitoring Project: New Technology Development - Radiant Barrier Pilot Project
Contract Report FSEC-CR-1231-01
Florida Solar Energy Center, Cocoa, Florida, January 2001

Reflective Insulation Manufacturer`s Association
Understanding and using Reflective Insulation, Radiant Barriers And Radiation Control Coatings
May 2002
www.rima.net

US Department of Energy, Energy Efficiency and Renewable Energy
Reflective Insulation
http://www.eere.energy.gov/buildings/info/components/envelope/insulation/reflective.html