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