Radiant barrier insulation © Daniel Friedman Reflective Insulation: properties, uses, technical data

  • REFLECTIVE INSULATION - CONTENTS: Reflective insulation in buildings, composition, installation & technical data. List of typical uses for reflective insulation. Technical data for single & double bubble foil laminated reflective insulation products. Definition of reflective insulation; definition of radiant barrier insulation; what's the difference between reflective insulation & a radiant barrier?
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Reflective insulation:

Properties, R-values, & uses of reflective insulation in buildings and in other applications. Where is reflective insulation used? Where is reflective insulation actually useful or effective?

This article describes the properties & uses of reflective insulation in buildings and other applications.

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Foil-based Reflective Insulation material identification, insulation R-values, insulation characteristics, applications, & technical data

Radiant foil barrier insulation installatin © Daniel FriedmanWhat's the difference between RADIANT BARRIERS[a separate article]

and REFLECTIVE INSULATION [discussed here] ?

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Watch out: In understanding insulation, radiant barriers, and reflective insulation products it's worth noting that you may find products labeled as "insulation" that are a simple single thickness aluminum foil radiant barrier, and you may find insulating blankets covered with aluminum or even kraft paper and aluminum labeled as a radiant barrier product. It's confusing.

A radiant barrier works principally by serving as a single layer of aluminum foil, possibly reinforced with fibers or paper backing, used to reflect heat outwards (keep the attic cooler) or inwards towards the building interior (avoid losing heat, keep the building warmer).

Reflective insulation is a similar insulating and energy conserving product that adds an air cushion, usually in the form of plastic bubble material, between layers of aluminum foil to improve the insulating value or R-value of what would otherwise be a simple radiant barrier.

We expand on these definitions at the end of this article.

Thickness & composition distinguish among radiant barriers (thin) and reflective insulation (thicker) and foil faced insulation (much thicker)

ALFOL radiant barrier insulation © Daniel FriedmanSome radiant barrier products may comprise multiple layers of aluminum foil or foil plus paper.

While the air layer trapped between these layers improves the R-value of the product, in our OPINION, products less than 1/4" in thickness remain, in our book, a radiant barrier.

Products that are made up of at least two layers of aluminum foil, separated by bubble or other material that is 1/4" thick or slightly thicker are reflective insulation.

The double-layer kraft and aluminum "ALFOIL house insulation blanket" shown at left works principally as a radiant barrier.

As we discuss at RADIANT BARRIERS, " Dead air trapped between the double layers of foil above the kraft paper provided a slight increase in the R-value of this product."

Still thicker insulating products, such as foil faced fiberglass insulating batts that are 1" or more in thickness, we refer to as foil faced insulation, not simple reflective insulation that will be described further here.

How is Reflective Foil Insulation Constructed - what layers, what materials?

Reflective insulation is usually made using two layers of aluminum foil that has been laminated or "glued" to the surface of two layers of plastic "bubble wrap" or air bubble material.

Layers of construction of reflective foil building insulation © Daniel FriedmanOr in some older reflective foil building insulation such as the "Double Layer" ALFOL Type II Double Layer insulating product shown at left, you may find as many as four layers comprised of

In newer reflective insulation constructed using a layer of bubble wrap, the rounded surface of the air bubbles keeps the two layers of foil separated and the individual bubbles, by trapping or enclosing air, ensure that there is a still-air insulating barrier between the two surfaces of foil, thus improving the R-value of the reflective insulating material.

The bubble-trapped air means that no air movement by convection should occur within the reflective insulation. Such air currents would reduce or even eliminate the R-value of insulation just as air currents in walls, floors, or ceilings will increase heat transfer through those structures.

When used under a roof or in an attic floor (not our first choice) the aluminum foil on both surfaces of the reflective insulation means that the same insulation layer will reflect heat outwards (back towards the roof) from the upper surface of the reflective insulation in summer, and it will reflect heat downwards or inwards (back towards the building interior) during the heating season.

Common Uses of Reflective Building Insulation

Unlike RADIANT BARRIERS that were used in lieu of fiberglass, mineral wool, or foam insulation in building floor, wall, or ceiling cavities, reflective foil based bubble-interior building insulation is not used in modern residential construction as the primary cavity insulation material. Rather the product is used in more industrial settings and in special applications as we list here:

Properties & R-Values of Reflective Insulation Products


Single Air Bubble Layer

Double Air Bubble Layer

R-value [b] 4.9 5.0
Reflectivity 0.96-0.97 0.96-0.97
Permeability effectively zero for foil effectively zero for foil
Emissivity 0.03-0.04 0.03-0.04
Fire Rating Class A/Class 1 Class A/Class 1
Temperature Exposure -60F - 180F -60F - 180F
Puncture resistance 63 psi 66 psi
Weight per sq. ft. 0.8 oz 1.25 oz


[a] Based on industry standard sheet [on file];
[b] R values obtained from a C236 hot box test.

Watch out! these ratings were taken from the entire building cavity including the surrounding air space and thus reflect the R-value of the wall, floor, or ceiling the cavity represented, not the R-value of the material itself. Because building construction and air leak properties vary widely we question these numbers.

The original document for double air bubble layer reflective insulation: 15 (D), 7.31 (H) and 5.4 (U), and for single bubble layer reflective insulation 14.5 (D), 7.0 (H), and 4.9 (U).

Question: do some reflective barrier products contain asbestos

Borg Warner ALFOL Aluminum Foil Insulation at InspectApedia.comI have been researching the internet for information regarding asbestos in reflective insulation:

Images attached.

We have a small baby and construction was going on while she was very little. So I am trying to find out the likelihood of this material containing asbestos?

Do you have any information other than this post on your web site? - Anonymous by private email 2017/12/12

Reply: Yes some but not all reflective barrier products included asbestos cloth, paper, or boards.

Researching an answer to your question we found that particulary in the U.S. between the 1930's and early 1960's a number of reflective barrier insulation products included asbestos paper or in other forms as both a reinforcement, for fire resistance, or for heat resistance.

I have added that information in this article at REFLECTIVE INSULATION RESEARCH.

Here is a typical example

The composite insulation of the invention comprises two or more sheets of insulating material such as metal foil, laminated metal foil and paper, asbestos, plastic, or paper. (Alexander et als 1957)

Note: By this information I am NOT claiming that the Borg Warner Type II ALFOL aluminum foil + kraft paper reflective insulation shown above in your photo is an asbestos-containing product. Patents from Borg Warner involving insulation were focused on the refrigeration industry (not cited here).

Other reflective barrier products patented by General Dynamics and other companies described inslating products included a variety of heat reflecting inslulating materials whose patent disclosures did not include the word "asbestos". (Clay 1970).

Question: identification of reflective insulation vs. radiant barriers

Reflective Insulation a multi layer reflective or radiant barrier (C) AC Can you by any chance help me identify this type of insulation ? I have never seen it before. Thank you in advance.

I myself would like to learn more about this stuff since it is the first time i have ever seen it and i am curious and would like to learn more. I spent many hours trying to find any thing about this product to no avail please send me a link to the thread so i can follow along . - Anonymous by private email, 2016/10/23

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The reflective insulation shown above was found by the reader and is reported to be installed in a single family home in Altadena California. The home was built in 1951.


Looks to me like an early radiant-barrier type "insulation" product. I'm unsure what sort of paper was used inside the foil to give it more air space and thus improve its insulating rating. On the off chance that the paper is an asbestos product I'd take care not to make a dusty mess. We discuss reflective insulation such as your product here at REFLECTIVE INSULATION.

Separately, at RADIANT BARRIERS we discuss a similar product, radiant barriers, another reflective product. What's the difference between reflective insulation and a radiant barrier? It depends on your information source, as not everyone will speak with equal precision.

Watch out: it's possible that the paper baffles shown in the reflective insulation in your photograph are asbestos paper.

Definition of radiant barrier

A radiant barrier is a single sheet of reflective foil used to reduce un-wanted heat loss or un-wanted heat gain by placing a heat reflecting material at a strategic location. In buildings that's typically in an attic and most-often on the under-side of roof rafters or on the upper side of an attic floor.

A radiant barrier might also be placed in a wall or over a basement or crawl area. Historically aluminum foil but perhaps reflective mylar in more recent applications.

Definition of Reflective Insulation

Reflective insulation improves on the concept of a radiant barrier by using two or more layers of heat reflecting material, typically bound together to form a blanket. The blanket may be simply hollow or it may contain internal baffles such as shown in our reader's photograph above. However you'll note that except for material used to provide individual air chambers reflective insulation is hollow.

Reflective Barriers on Other Insulating Products

Other fiberglass insulating products are sold with a non-reflective kraft-paper facing that also aids insulation installation as well as sold as un-faced fiberglass batts. Products that combine a reflective barrier with fiberglass or another insulating material may be referred to as "reflective fibrous insulation" (Fay 1988).

Foil-faced fiberglass insulation is a more-widely-used contemporary insulating product found in building roofs, ceilings, attics, walls, floor. This product combines a foil faced paper on one side of the insulation. The foil facing improves the insulation's perfomance by reflecting heat as well as by serving as an air barrier, and the facing also aids in insulation installation by providing a paper flange that canb e stapled to the building framing rafters, ceiling joists, wall studs, or floor joists.

Unlike reflective insulation, foil-faced insulation combines the foil facing with a thickness of insulating material, typically fiberglass batts.

Research on Reflective Insulation

Heat reflective inslation, Benedict patent 1937 (C) InspectApedia.comWhile the insulating properties of multi-layer or multi-wall metallic materials are reflected in earlier patents ca. 1900, a surge of multiple-layer metallic reflective insulating materials began in the United States in the 1920's, possibly with the development of improvements in the economical production of thin aluminum sheeting or foils.

Borg Warner ALFOL Reflective Insulation with Kraft Paper at

Reflective insulation patented by Olsonin 1929 (C)


Continue reading at RADIANT BARRIERS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




Or see INSULATION R-VALUES & PROPERTIES - R-values & U Values of various materials

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