How Do Radiant Barriers Work

Radiant barrier foil insulation is a reflective insulation system that offers a permanent way to reduce energy costs. Radiant barrier foil insulation systems BLOCK radiant heat energy instead of absorbing it like fiberglass insulation.  Radiant barrier reflective foil insulation is unaffected by humidity and will continue to perform at a consistent level no matter how humid it may be. A radiant barrier foil insulation system is a layer of foil facing an airspace and is installed in the envelope of a building.

In order to fully understand how radiant barriers work and how they can benefit you, the following information has been comprised to provide a foundation for your new radiant barrier knowledge and understanding.

How Heat is Transferred

Heat moves from one location to another in three different ways: conduction, convection, and radiation.

  • Conduction:  this method of heat transfer occurs when two solid objects touch each other.  The heat is transferred between the two objects via molecular motion.  For example, if your hand touches the surface of a light bulb, the heat from the glass will be transferred to your hand.
     

  • Convection:  heat that moves through fluids, such as water, rising heated air, or steam is doing so by the convection. In air, convection results in rising heated air causing the cooler air to drop to the floor.  This creates what is called a free convection loop.  One can create their own convection loop by using a fan to circulate the air in a room. This creates what is called a forced convection loop.
     

  • Radiation: heat that is transferred by infrared waves is called radiation.  These rays are invisible to the naked eye and are not affected by air flow. Stepping out into the sun on a hot day, you will feel your skin heat up from the heat radiating from the sun. And you will still feel these heat rays regardless of how windy it is outside. Radiation is the transfer of heat from a warmer object across an air space (or vacuum) to a colder surface and all objects radiate some of their heat in varying degrees from 0% to 100% whether it be the surface of a car that's been sitting in the sun or an electric stovetop burner.

Other examples of radiant heat transfer:

  • Roof shingles which have absorbed heat via radiant heat transfer from the sun.

  • Heat radiating from a furnace.

Conventional Insulation

Most people are familiar with traditional insulating materials such as fiberglass, cellulose, Styrofoam, and rock wool.   These products absorb or slow down convective and conductive heat transfers to insulate.  These types of insulation do not BLOCK heat - only slow it down.  Therefore, after a period of time, 100% of the heat absorbed would eventually transfer through the insulation.  The rate in which this heat eventually transfers through an insulation material is the material's R-Value.

  • Fiberglass and blown-in cellulose insulation are manufactured with air spaces inside designed to reduce heat conduction through the material. They also restrict heat transfer by convection  by trapping air flows and lowering air circulation.

  • Similar to fiberglass and blown-in insulation, some foam insulations,  comprised of  hydrochlorofluorocarbons (HCF), also absorb conductive and convective heat.  However, HCF's found in some foam insulation products have been found to be extremely potent greenhouse gases and are being phased out by the United States over the next 23 years. 

How Radiant Barriers Work

A radiant barrier is designed to BLOCK (reflect) radiant heat energy unlike traditional insulations that are designed to slow it down by absorbing it.   A radiant barrier can also REDUCE heat transfer caused by convection by blocking convective air flow.

How does a radiant barrier reflect/BLOCK radiant heat?

There are two physical properties of aluminum that a radiant barrier utilizes to reduce the transfer of radiant heat.

  1. Reflectivity = The natural reflectivity property of a reflective surface facing a heat source across an air space allows the aluminum to REFLECT radiant heat back to the direction from which it came.

  2. Emissivity = All materials have emissivity's ranging from 0% to 100%.  The lower the emittance percentage of a material, the lower the amount of radiant heat radiated from its surface.  The naturally low emissivity property of a reflective surface facing an air space results in very low emittance of heat from itself; it does not radiate much of its own heat from itself.

candy bar wrapper
Example of reflectivity property in common every day uses.  This aluminum keeps the chocolate from getting too warm and melting.

A Radiant barrier REFLECTs radiant heat that strikes its surface across an air space from a heat source and conversely, it EMITs very little radiant heat from its surface across an air space opposite a heat source.

Why Radiant Barriers REQUIRE An Air Space

No matter how you plan to install a radiant barrier, it MUST have at least one air space of at least 3/4 of an inch on either side to be effective at BLOCKING radiant heat.  It does NOT matter which side of the radiant barrier the air space is located.  The purpose of the air space is to prevent conductive heat transfer.

If a radiant barrier does not have at least ONE air space on either side of it, heat will conduct from the surface touching the radiant barrier, through the barrier, and then transfer to the next surface touching the radiant barrier on the opposite side therefore, giving you no protection against the heat you intend to block.

Therefore, as long as the air space requirement is achieved, a radiant barrier will be effective at BLOCKING radiant heat regardless of your application, i.e. interior/exterior walls, siding, roofing and attic locations, etc.

What Happens When No Air Space Exists

Because a radiant barrier requires an air space on at least one side of itself to be able to BLOCK radiant heat, a radiant barrier CANNOT be installed directly underneath roofing materials where no air space exists.

For example, if you install a radiant barrier on top of roof decking between the felt paper and asphalt shingles, it will NOT provide any benefits as the radiant heat would be transferred through the shingles, through the felt to the radiant barrier, and through the roof decking into the attic space (see image below).

radiant barrier on shingles

A radiant barrier can be effective with an asphalt shingle roof ONLY when installed inside the attic either to the underside of the roof decking or to the underside of the roof rafters.  In these attic space applications, there is an air space below the radiant barrier.  It is the existence of a single air space that eliminates, almost entirely, the pass-through of radiant heat.

Our RadiantGUARD® radiant barriers REFLECT 95-97% of the radiant heat that strike their surface across and air space and conversely only EMIT 3% of the radiant heat from their surface facing an air space.

Everyday Example of Low Emissivity Across an Air Space

The help you understand the more difficult concept of emissivity, imagine of a hot baked potato wrapped in aluminum foil.  If you hold your hand close to the wrapped potato (not touching it), you would feel very little radiant heat coming off the aluminum because aluminum doesn't “emit” much heat across an air space (aluminum has a low emissivity factor).  If you were then to touch the aluminum wrapped baked potato, you would feel a great deal of heat because the aluminum would then be conducting heat from the potato, through the aluminum, to your hand.  Because you have lost the air space, the heat would contact (conduct) to your hand.

A radiant barrier is ONLY effective when at least a 3/4" air space is provided on either side of itself regardless of the location of the heat source.   If the air space is on the side of the heat source, the REFLECTIVITY property works to REFLECT the radiant heat.  If the air space is on the opposite side of the heat source, the low EMISSIVITY property works to reduce the amount of radiant heat that EMITs from its surface.

Blocking Radiant Heat Transfers in a Home or Building

All building surfaces include roofs, ceilings, and even conventional fiberglass and blown-in insulation radiate heat in varying degrees.  Radiant heat from the sun strikes the outer surfaces of roofs and walls and is absorbed causing building surfaces to heat up.  This absorbed heat moves through the material (via conduction) to the opposite side and is then radiated from itself into attics and living spaces increasing the temperatures inside the building.

Installing a radiant barrier is a MUST to combat the major form of heat transfer (radiant)  that is currently not being controlled by your conventional insulation.

What Classifies as a Radiant Barrier

Per the Department of Energy (DOE), a product classified as a "radiant barrier" MUST have a low emittance of 10% or less and a high reflectance of 90% or more.

RadiantGUARD® radiant barriers have an emittance of only 3-5% and a reflectance of 95-97%; considerable better than the DOE's radiant barrier minimum classification requirements.  For more information, visit the Department of Energy website.

How RadiantGUARD® Radiant Barriers Benefit You

RadiantGUARD® radiant barriers reflect/BLOCK radiant heat; not just absorb or slow it down like other forms of insulation.

RadiantGUARD® radiant barriers are unaffected by humidity or ambient temperatures, unlike other forms of insulation, and therefore, perform at a consistent level at all times.

RadiantGUARD® radiant barriers reflect/BLOCK 95-97% of the radiant heat transfer and when installed in an attic space, they can result in a reduction of attic temperature below the radiant barrier of up to 30 degrees.  Lowering the temperatures above living space ceilings provides a significant benefit by reducing air conditioning loads and energy usage.  Our radiant barriers can:

  • Reduce heat transfer from attic to living spaces by 16-42%,

  • Extend the life of air conditioning unit,

  • Increase the comfort level of a home or building, and

  • Reduce monthly cooling bills up to 17%.

RadiantGUARD® radiant barriers are safe and easy to install:

  • No breathing apparatus required

  • Non-toxic / non-carcinogenic

  • Clean and lightweight; easy to handle

  • Installation requires no special tools or clothing

  • Don't promote the growth of fungi or bacteria

  • Provides no nest support for rodent or insect pests

  • Class A / Class 1 Fire Rating

  • Meets fire and smoke safety requirements of most federal, state and local building codes

  • Require no maintenance

  • Do not shrink

RadiantGUARD® Testing and Approvals:

  • United States Testing Company

  • Tennessee Valley Authority

  • Tennessee Technological University

  • State of California Quality Standards

  • Oak Ridge National Laboratory

  • Metro Dade County

  • Texas A&M University