Reflective Insulation

Fire and Thermal Performance

This article will analyze the fire and thermal performance capabilities of insulation approved for steel building application. Capital Steel Industries continues to include this and other essential insulation information on our website to inform consumers about the steel building industry and related products.

More and more consumers, investors, and owners understand the importance of adequately insulating a new steel building. However, the performance of the insulation can actually be deficient if it is not specifically designed for a steel structure. This is particularly seen in the established thermal and fire performance indices.

Many insulation manufacturers claim that they meet fire safety code requirements with their products. However, some reflective insulation products manufactured with plastic cores do raise safety issues because of their performance under fire test simulations.

Stated vs. Actual Performance

A few insulation manufacturers make claims about their products’ performance based on “laboratory” results. The performance results, however, in this setting do not always reflect “real world” comparison of how the insulation will react in a steel building setting.

Fire Safety

Suitability for a particular reflective insulation in a steel building application largely revolves around fire safety. A flame spread index of 25 or less under tunnel testing is required by most building codes. A good low flame spread index initially can be overshadowed by a burn test that causes the materials to delaminate, drip, or melt. Flame-over conditions may, in fact, be generated by these materials. Fitness of use of these reflective materials comes into question with these less than desirable results.

Testing for Thermal Performance

Thermal performance results rarely give an R-value rating to the insulation based on the material alone. It also takes into account the total construction environment. Test methods have been developed recently that quantify the thermal performance of the component materials along with construction assemblies.

Evaluating Thermal Performance

It is important to have low-emittance facing materials along with a smooth sealed air space that inhibits air exchange and movement to maximize the thermal performance of reflective insulation. Optimal conditions can throw off an R-value of up to 10. R-value is substantially lower, however, if the direction of the heat flow changes, the facing emissivity is degraded, less than 3 1/2 inches of air space is available and/or there is not a thorough seal to the air space.

Actual Versus Ideal Scenarios


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Manufacturer supplied values for reflective foil must be analyzed carefully because normally those values were obtained in a laboratory setting. The heat transfer value across an air space is normally a product of the combination of the conduction, convection, and radiation measurements. However, having a true leak-free uniform air space is almost impossible in a steel building interior environment. R-values, then, are inconsistent. Non-accounting for real world effects is also seen in summer and winter testing environments which reflect R-values reduced anywhere from 25 to 50% from the manufacturer’s stated values.

Insulation Emissivity

Insulation performance is also dependant upon emissivity. Superior performance emissivity values initially of bright foil surfaces can be degraded by aging, dust contamination, oxidation, or proximity to polluted areas. This increases the emissivity which decreases the thermal resistance.

Reflective Insulation Layers

Many manufacturers market insulation and speak to the high performance characteristics of multiple layers. However, the actual additive qualities of this approach have been suspect in testing.

Compliance to Energy Codes

Energy code compliance by builders may involve the use of “worst-case” conditions as manufacturer’s claims for insulation performance are the only gauge. Again, these values are the result of a lab environment and not necessarily the conditions of a steel building interior that a builder must deal with.


Thermal performance can vary between the manufacturer’s claims and the actual environment that insulation is exposed to. Additional questions about insulation and its application in steel buildings can be answered by Capital Steel at 800-246-9640.