All exterior walls of your home or building should be insulated. Insulation is a key component of the building envelope and will have a major impact on both energy efficiency and the comfort level inside. Proper wall insulation will reduce heat losses to the outside in winter and prevent radiant heat from penetrating the building in summer. Insulating walls will also provide air sealing, reducing both drafts and the water vapor carried inside with drafts.

Building materials vary widely in their ability to resist the transfer of heat. Metal, for example, is a very good conductor of heat. Materials that do not conduct heat well are used for insulation. Air is an excellent insulator. Houses are built with air cavities in the walls and the attic to resist the flow of heat. Most houses built in the 1930s or later have cavity walls (prior construction had solid walls). Cavity wall insulation reduces heat loss through the walls by up to 40%. The best time to insulate wall cavities is during new construction or during major renovations to either interior drywall or exterior siding.

Heat flows from a warm medium to a cold medium in three ways:

• By radiation from a warm surface to a cooler surface through air or a vacuum using infra-red heat rays. Most radiant energy striking a building comes from solar radiation.
• By conduction through solid or liquid materials resulting from direct contact.
• By convection, which involves the physical movement of air - warm air rises. As air warms it will expand creating pressure to move outward through the walls.

Heat moves through wall cavities by a combination of radiation, conduction, and convection with radiation being the dominant method of heat transfer. Research shows that control of radiant heat transfer is the core of heating/cooling climate control. Radiation accounts for 65-85 percent of all heat transfer through walls.

Traditional insulation materials use air spaces between fibers or in plastic foam bubbles to trap expanding warm air and prevent it from escaping the building. Reflective insulation uses fibers, foam or bubbles sandwiched between two layers of reflective aluminum foil sheeting to effectively block both radiation and convective heat transfer. Reflective insulation installed as a radiant barrier is essential in warmer climates to reduce air conditioning requirements.

Insulation is rated by its ability to resist both conductive and convective heat flow in units called R-value. R-value gives the insulation resistance per inch of material. Construction materials with higher R-value ratings are more effective insulators than materials with lower ratings for the same thickness. For example, heat will flow through an R-12 insulated wall only half as fast as through an R-6 wall.

The US Department of Energy recommends that exterior walls be insulated to a minimum of R-13 in the South up to R-22 in New England. Reflective insulation has the highest R-value per inch of any insulation on the market. At R15.67 (details), reflective insulation can be used either alone or in conjunction with foam or mass insulation in colder climates to stop both radiant heat transfer and convective heat transfer.

 Reflective insulation and fiberglass batt installed together

 Click here for a comprehensive article on insulation R-values. 

While other types of insulation are made to resist or impede the flow of warm air, reflective foil insulation reflects back 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. Reflective insulation is commonly made of two layers of aluminum foil sheeting with foam or plastic bubbles in between creating an air space to also resist convective heat transfer. The aluminum foil component in reflective insulation will reduce radiant heat transfer by as much as 97%.

Prodex Foil-Foam-Foil R-15.67 details Reflective Insulation

Click here for a comprehensive article on the Physics of Foil.

 Radiant barrier

 All new buildings should incorporate a radiant barrier as part of the insulation system. The concept is simple: each unit of radiant heat energy that is reflected away from your building in summer, and each unit reflected back in during winter, means less operation of your heating and air conditioning systems, less wear and tear on your equipment, and less money you pay in utility costs. Use either a foil radiant barrier or reflective insulation. Radiant barriers (aluminum foil with no center layer) become reflective insulation because they face an air space like an attic, wall cavity or crawlspace. Radiant barriers primarily impede the downward flow of radiation. The largest benefit of using a radiant barrier is reduced air-conditioning costs in warm climates.

Click here for a comprehensive article on radiant barriers.

 Vapor barrier

 A vapor barrier (or more accurately, vapor diffusion retarder) is an essential part of the moisture control strategy for a home. The primary purpose of a vapor barrier is to keep moisture from getting inside your walls. Condensation within the walls can cause wood rot, mold, mildew and fungus growth. A vapor barrier acts as a physical shield to repel moisture. In addition to its properties as a radiant barrier, reflective insulation can be used as a vapor barrier. When properly installed, waterproof reflective insulation can reduce or eliminate condensation. As reflective insulation is non-absorbent, it will not mildew or promote fungus growth.

In colder climates, a vapor barrier should be placed on the interior or warm side of the wall. The US Department of Energy map below shows that in some southern climates, the vapor barrier should be omitted, while in hot and humid climates, such as along the Gulf coast and in Florida, the vapor barrier should be placed on the exterior of the wall.

Source: Wall Insulation, US Department Of Energy DOE/GO-102000-0772 October 2000.

 Click here for a comprehensive article on using a vapor barrier in you home.

 Air infiltration barrier

 Air sealing and moisture control make a building more comfortable inside and save energy by making insulation more effective. A significant amount of moisture enters walls through air leaks and capillary action from the ground below. Installation of house wrap will prevent moisture from penetrating from the outside.

When properly installed, reflective insulation will act as an air infiltration barrier thereby sealing the wall to reduce heat loss from expanding warm air and prevent water vapor in the air from entering the wall cavity. The US Department of Energy estimates that in a 100-squarefoot wall, one cup of water can diffuse through drywall without a vapor barrier in a year, but 50 cups can enter through a ½-inch, round hole. Sealing air leaks is estimated at 10 to 100 times more important than installing a vapor barrier.

The benefits of using reflective insulation instead of conventional bulk insulation are numerous.

• Radiant barrier - reflects 97% of radiant heat
• Clean, Lightweight, Flexible & Very Strong
• Saves money and energy
• Very thin - can be used effectively in small spaces or over framing members
• Easy to install
• Installation requires no special tools or clothing
• Easier to cut than fiberglass batt and bubble wraps
• Convenient flange tabs on sides
• Can be stapled, nailed, glued or sewn
• Non-hazardous/Non-toxic/Non-carcinogenic
• Safe for workers to use as there are no fibers to breath or cause skin irritation
• Provides up to 19 DB of soundproofing
• Works in temperatures extremes as low as (minus) -20 degrees Celsius and as high as 80 degrees Celsius (and if an air space is added it can go up to 300 degrees Celsius)
• Vapor Barrier, waterproof, non-absorbent - reduces or eliminates condensation when properly installed
• Does not promote mold, mildew or fungus growth
• Does not provide nesting for birds, rodents or insects
• Provides Class A/Class 1 fire rated protection - meets fire and smoke safety requirements of most federal, state, and local building codes
• UV resistant
• Flexible at low temperatures
• Withstands fluctuations in outdoor temperatures
• Reinforced (Commercial Grade)
• Reduces potential for ice dams

• Reflective insulation has higher R-values (or resistance to heat transfer) than any other type of insulation per inch. ¼" thick reflective insulation has more insulation value than 6 inches of common fiberglass batt. Foil-FoamFoil insulation has an R-value of 14.5.
• Reflective insulation is the only type of insulation that reflects radiant heat. Traditional fiberglass insulation has no effect on radiant heat transfer. Estimates are that between 80% and 90% of the radiant heat striking fiberglass will pass right through it. Aluminum foil reflective insulation, which can reflect up to 97% of the radiant energy that strikes it, has proven to be an outstanding radiant heat barrier.
• Reflective insulation is the only type of insulation that can be used as a vapor barrier. All other insulation requires the addition of a separate vapor retarder to prevent moisture accumulation in the walls and ceilings that can cause rot, mold, fungus, and dripping.
• Reflective insulation will not compress or absorb moisture - conditions that seriously degrade the performance of both batts and loose-fill insulation.

Install on the inside of the wall in cooler climates and outside under the exterior sheathing in hot/humid climates like the Gulf coast. Install un-perforated reflective insulation on the interior and perforated reflective insulation on the exterior so moisture can diffuse to the outside. Installing un-perforated reflective insulation on the exterior could trap moisture inside the wall.

 Wood frame walls

 Reflective insulation can be installed over wood framing members, not just in between them, to mitigate thermal bridging of heat through the wood itself. Wood is a poor insulator. As wood framing makes up 12-25% of the total surface area of a wall, preventing thermal bridging can result in significant energy savings.

 Metal frame walls

 The home building industry has seen an increasing use of steel framing for new home construction in recent years. Steel buildings are growing in use for both commercial and residential applications. As metal is a better conductor of heat than wood, even more thermal bridging can occur with metal than wood framing. Insulation installed over the framing is critical for a steel building.

Exterior Finishing Air Space Rigid Insulation 1" Drywall (Fire Retardant) Metal Studs Reflective Insulation Metal Strapping Drywall Anti-convection shield at mid-height or every four feet high made with Reflective Insulation

Click here for reflective insulation installation instructions in commercial and residential applications.

CUS Department Of Energy,
Wall Insulation,
DOE/GO-102000-0772, October 2000.

Kansas State University,
Residential Insulation,
January 2000.

Reflective Insulation Manufacturer's Association,
Understanding and using Reflective Insulation, Radiant Barriers And Radiation Control Coatings,
May 2002.