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?
  • POST a QUESTION or READ FAQs about reflective insulation used in buildings, mechanical systems, & other locations;

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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] ?

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.

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?

Layers of construction of reflective foil building insulation © Daniel FriedmanReflective 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.

Or 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

  • Kraft paper (outer layer, printed with the company's information (at the bottom in our photo)
  • A doubled layer of kraft paper, possibly coated on one side with a bituminous moistdure barrier
  • A layer of aluminum foil (at the top in our photo).

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:

  • Animal barns, poultry buildings, stables
  • Commercial buildings, garages, workshops
  • Concrete curing blankets
  • Garage door lines
  • HVAC duct wrap, especially as a retrofit product
  • Packaging for products that need to be protected from temperature extremes during shipping
  • Storage facilities
  • Survival blankets
  • Temporary-occupancy buildings such as temporary jails or shelters
  • Transportation truck and trailer cargo liners
  • Window coverings or insulating window shades
  • And in these special applications:
    • Reflective insulation boards or blankets behind freezers, woodstoves [watch out, overheat risk, may not be UL approved],
    • behind radiators,
    • behind refrigeration and air conditioning coils inside of HVACR equipment


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).



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