Radiant Barriers 101 - Increase Your Understanding
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
How Heat is Transferred
Heat is transferred from one source to another via three
methods of transfer: conduction, convection, and
the transfer of heat flowing through a substance (molecular motion) or to
another touching substance. If you touch a pot on the stove, the
heat is transferred from the pot to your hand via conductive heat transfer.
the transfer of heat in fluids, such as rising heated air, steam, and moisture. If you put your hand above a boiling pot, you will feel heat
rising from the pot in the form of steam. This transfer of heat from the pot
upwards is via convective heat transfer. Convective heat transfer
results in warmer air rising and cooler air settling creating a convection
loop termed free convection. A Convection loop can also be
generated mechanically with the aid of fan or wind and is then called
Radiant: the transfer of heat via infrared radiation rays that are invisible to the
naked eye and unaffected by air currents.
If you step outside on a windy sunny day, you will feel the sun's heat rays on
your face. This transfer of heat from a heated source across an air space to
a colder surface is via radiant heat transfer. All materials radiate
radiant heat in ranges from 0% to 100%.
Common examples of radiant heat transfer:
Skin warming up when outside on a sunny day via the
radiant heat from the sun regardless of the ambient temperature.
Roof shingles heated via the radiant heat from the
Heat radiating from a light bulb.
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
Fiberglass and blown-in cellulose insulation rely on
air spaces within the material to decrease the conductivity of heat.
They also reduce convective heat flows by trapping heating air flows and
thereby restricting air circulation.
Foam insulations work similarly to fiberglass and
blown-in insulation. Some foam insulations use hydrochlorofluorocarbons
(HCF) to absorb and slow down the transfer of heat via
conductive and convective measures. However, the United States has
scheduled phasing out the manufacturing and importing of all HCFs over
the next 23 years. HCF's, such as those contained in some foam
insulation products, are considered very potent greenhouse gases.
How Radiant Barriers Work
A radiant barrier reflects/BLOCKS radiant
heat energy instead of trying to absorb it. A radiant barrier
REDUCES convective heat transfer by acting as a physical blockade against
convective air flow.
How does a radiant barrier reflect/BLOCK radiant heat?
The reflective surface of radiant barriers has two
properties that enable it to reflect/BLOCK radiant heat when at least
one air space is provided on one side:
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.
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.
Example of reflectivity property in common every day uses.
This aluminum keeps the chocolate from getting too warm and
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
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
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.
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
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.
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
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