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What is Radiant Barrier?

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Radiant barrier is a highly reflective material, typically made of aluminum, which blocks the transfer of radiant heat by reflecting it away from its surface offering a permanent way to reduce your monthly utility costs. Radiant barrier foil insulation systems BLOCK radiant heat energy instead of absorbing it like fiberglass insulation.  Because this foil insulation is unaffected by humidity, it will continue to perform at a consistent level no matter how humid the seasonal climate. 

A radiant barrier insulation system is a layer of reinforced aluminum foil facing an airspace inside a building.  

How Does Radiant Barrier Work?

In order to fully understand how a radiant barrier works and how one can benefit you, the following concepts and radiant barrier information will enhance your understanding.

Heat Transfer Methods

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

Other examples of radiant heat transfer:

How Conventional Insulation Works

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.

How Radiant Barrier Works

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.

aluminum candy bar wrapper
Example of aluminum reflective 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).


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.

radiant barrier under shingles

radiant barrier decking

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.

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:

RadiantGUARD radiant barriers are safe and easy to install:

RadiantGUARD Testing and Approvals: