Radiant Barrier FAQ: Answers to Your Top Questions
Frequently asked questions
A radiant barrier is a highly reflective, low-emissivity material, typically made with aluminum foil, designed to block radiant heat transfer. To qualify as a true radiant barrier, a material must have an emissivity of 0.10 or less, meaning it emits very little radiant heat from its surface. It also must have a reflectivity of 90% or greater, reflecting the vast majority of radiant heat back towards its source.
In the summer, the sun produces radiant energy that travels through space and our atmosphere until it is absorbed by the roof of a home. The heat conducts through the roof deck which then radiates downward toward the insulation below; a radiant barrier between the roof and insulation reflects that heat back toward the roof deck before it can be absorbed by the insulation, reducing the amount of heat transferred toward the living space below.
Radiant heat travels only through air or through the vacuum of space as electromagnetic radiation. Without an air space adjacent to at least one foil surface of the radiant barrier, heat transfers directly from one solid material to another by conduction rather than being emitted as thermal radiation across an air space. In practical terms, without an adjacent air space, no radiant heat has been emitted and there is no radiant heat at the foil surface for the radiant barrier to reflect in the first place.
A radiant barrier doesn't have its own R-value because R-value measures resistance to conductive heat transfer, while radiant barriers reduce radiant heat transfer. However, reflectivity and emissivity specs are helpful measures of radiant barrier effectiveness. Also, equivalent R-values can be calculated for assemblies using radiant barriers based on factors such as the direction of heat flow and the depth of the adjacent air space.
Yes. The tiny perforations make up only a very small percentage of the radiant barrier's total surface area, so they have virtually no effect on its ability to reflect radiant heat. The perforations allow water vapor to pass through the radiant barrier, however, which helps prevent moisture from becoming trapped and makes perforated attic foil the preferred choice for most attic applications.
A double-sided radiant barrier is more effective when there's an air space adjacent to both faces of the foil. A Texas A&M test published by RIMA International showed that a two-sided radiant barrier reduced heat flux substantially more than a comparable one-sided barrier in the tested attic assembly.
Untreated aluminum can reflect up to 97%, but it oxidizes quickly and loses that reflectivity within a few years. ArmaFoil™ is pre-coated to resist oxidation, so its 95% reflectivity holds steady for the lifetime of the product — a stable 95% generally outperforms a 97% that degrades over time.
Emissivity is an important measurement when comparing radiant barriers. The best radiant barrier paints (also known as Interior Radiation Controlled Coatings or IRCCs) test around 0.16 emissivity (roughly 84% of heat is blocked), while ArmaFoil™ tests near 0.05, blocking closer to 95% of radiant heat. Paint products can be easier to apply in certain applications (particularly in attics with very low-pitched roofs), but for maximum radiant heat reduction, aluminum radiant barrier foil products are significantly more effective than IRCC paint products.
For the vast majority of our customers, cell signal degradation is not an issue after installing a radiant barrier. In our experience, customers have only reported problems when the cell signal was already weak and, typically, when a radiant barrier was installed in both the walls and attic. At the time of this writing, we have never received a customer complaint regarding Wi-Fi signal degradation caused by a radiant barrier installation.
Yes. Heavier does not necessarily mean stronger. Unlike traditional radiant barriers that laminate foil or metalized film onto a plastic layer, ArmaFoil™ uses a vacuum deposition process that bonds aluminum directly to a strong polyethylene fabric without heat lamination. Traditional heat lamination requires the plastic base material to be heated to its melting point, which can stress the material and cause it to become more brittle. Because ArmaFoil™ isn't subjected to this heat-lamination process, it can be made from a lighter-weight material while still providing excellent tear and staple strength. The result is a strong, flexible radiant barrier that does not become brittle or “zipper” when torn.
ArmaFoil™ combines high reflectivity, low emissivity, excellent tear strength, and a lightweight construction that makes it easier to install and more reliable over time. Its unique manufacturing process produces a strong, flexible material that resists tearing and “zippering” around staples. Our contractors particularly appreciate that its lightweight design puts less stress on staples, and in their experience, the combination of light weight and high tear strength prevents ArmaFoil™ from pulling through staples over time. ArmaFoil™ is also designed to resist oxidation, is backed by a 25-year warranty, and is made to provide effective radiant barrier performance for the life of the home.