Our radiant barrier foil is the best on the market. We source our foil at Atticfoil.com who for years has sold attic foil direct to consumers and has found the strongest most durable and shiny attic foil available. It is the 28.6 lb. roll and has to be cut with a razor knife and you cannot tear it with your hands. For a sample click here:
Here are the product specs:
|Product||double-sided (single sided foil radiant barrier also available), reflecting, 99% pure aluminum foil with inner woven polyethylene scrim|
|Weight||28.6lb per 1,000 square foot roll +/- 2%|
|Tensile Strength||test method ASTM D-828|
|Machine Direction||83.7lb/in width|
|Cross Direction||70.1lb/in width|
|Flame Spread||10 ASTM E84|
|Fire Rating||class A/class 1 ASTM E84|
|Smoke Development||10 ASTM E84|
|Water Vapor Permeability||72g/m 2/24hr; 14 perms ASTM E96|
|Temperature Range||76°F to 212°F ASTM C411|
|Thermal Properties||emissivity 0.03 (reflects 97% of infrared heat) ASTM E408|
A radiant barrier's performance is determined by two factors:
Emissivity (or emittance) – the ratio of the radiant energy (heat) leaving (being emitted by) a surface to that of a black body at the same temperature and with the same area. It's expressed as a number a between 0 and 1. The higher the number, the greater the emitted radiation. Our foil has an emissivitiy of .03 or basically it lets 3% of the radiant heat through.
Reflectivity (or reflectance) – a measure of how much radiant heat is reflected by a material. It's also expressed as a number between 0 and 1 (sometimes, it is given as a percentage between 0 and 100%). The higher the number, the greater the reflectivity. Our foil reflectivity is 97%.
How the radiant barrier foil works:
Radiant barriers are installed in homes and businesses —most commonly in attics—to reduce summer heat gain and winter heat loss, which helps lower heating and cooling costs. The barriers consist of a highly reflective material that reflects radiant heat rather than absorbing it. They don't, however, reduce heat conduction like thermal insulation materials.
Heat travels from a warm area to a cool area by a combination of conduction, convection, and radiation. Heat flows by conduction from a hotter material to a colder material when the two materials touch. Heat transfer by convection occurs when a liquid or gas is heated, becomes less dense, and rises. Radiant heat travels in a straight line away from the hot surface and heats anything solid as the wave of energy hits it.
When the sun heats a roof, it's primarily the sun's radiant energy that makes the roof hot. A large portion of this heat travels by conduction through the roofing materials to the attic side of the roof. The hot roof material then radiates its gained heat energy into the cooler attic (some of the roof's heat will radiate in other directions too). A radiant barrier reduces the radiant heat transfer from the roof to the attic space. In our product's case, by 97%.
The angle the heat wave strikes the surface—a right angle (perpendicular) usually works best. That's why we staple it against the rafters of the attic.
All radiant barriers must have a low emittance (0.1 or less) and high reflectance (0.9 or more). RADIANT PAINT EMITS .25 AT BEST SO IT'S NOT A RADIANT BARRIER. Of these factors, the angle the heat wave strikes the surface has the most influence on how well any shiny surface acts as a thermal insulator. From one brand of radiant barrier to another, the reflectivity and emissivity are usually so similar that it makes little difference as far as thermal performance. (Most products have emissivities of 0.03–0.05, which is the same as a reflectivity of 97%–95%.) Also, the greater the temperature difference between the sides of the radiant barrier material, the greater the benefits a radiant barrier can offer.
Greenlows installs all their foil products directly to the rafters of the roof using staplers. In most cases, we will "flat-top" the top portion of the foil creating a sub attic on the back side of the foil that collects the heat for the exhaust mechanisms to manage.
Radiant Barrier Foil is Superior to Reflective Coatings or "Radiant Barrier Paint"
There are several suppliers of products misnamed "radiant barrier paint" that are designed to be sprayed on the underside of the roof decking in the attic. These "radiant barrier spray" products are paint solutions that include aluminum metallic flake additives designed to reflect heat.
So called "radiant barrier paint" products are NOT true radiant barriers per the US Department of Energy.
The EPA does not label paints and coating for the inside of roof decks (or attic) in the insulation program because paints and coatings do not meet the Federal Trade Commissions (FTC) definition of “home insulation.” The EPA qualifies paint only as a roof coating in our Roofs program (generally used for the top of a commercial building roof). Roof coatings are NOT insulation. They reflect solar heat off a roof rather than absorbing it keeping the building cooler.
The EPA DOES qualify radiant barrier foil as ENERGY STAR because it meets the FTC definition of home insulation. (read more about what the EPA says about these spray paints):
Radiant Barrier Definition : Per the Department of Energy (DOE), a product classified as a "radiant barrier" must have a low emittance of 10% or less and high reflectance of 90% or more.
"Our foil insulation products have an emittance of 3% and a reflectance of 97%; far exceeding the DOE's radiant barrier minimum classification requirements. For more information, visit the Department Of Energy website."
These spray paints do not come close to Department of Energy's definition for a radiant barrier.
David W. Yarbrough, Phd, PE of the Reflective Insulation Manufacturers Association (RIMA) tested the reflectivity and its converse (emissivity) of 16 leading radiant barrier paints and presented his results on June 20, 2006. As you can see from the testing results below, the emittance of radiant barrier paints is varied across manufacturer and products. ** NOTE: Only 4 of the products actually satisfy the ASTM requirements set forth for an interior coating intended to reduce radiant heat transfer to and from the coated surface.
Radiant barrier foils emit only 3% making them FAR SUPERIOR to radiant barrier paints.
Below are the results of the RIMA radiant barrier test. The full test can be viewed here: