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What is the Best Insulation to Put in a Metal Building?

Fiberglass has been a popular insulation solution for metal building systems over the years because it has low installation costs per R-value.

However, fiberglass insulation is used to slow down the loss or gain of heat within a metal building. It provides a barrier between the inside of the metal and the significantly different temperatures outside of the metal building. Radiant barrier or foil insulation differs from fiberglass insulation in that, instead of slowing down the process of heat transfer, it blocks and reflects heat.

R-value versus Emissivity

Fiberglass insulation’s resistance to heat transfer is measured by an R-Value. Of course, R-Values refer only to conductive heat transfer.

Radiant Barrier’s heat resistance is measured by emissivity. Emissivity only measures radiant heat resistance.

The predominate heat transfer a metal building experiences in the summer months is from the radiating heat of the sun.  In fact, 93% of the heat gain that a metal building experiences in the summer months can be attributed to radiation. During the winter months, 75% of a metal building’s heat loss can be attributed to radiation.

Fiberglass insulation can be 90% emissive. Which means 90% of the radiant energy that meets the fiberglass is transferred through the insulation into the interior of the metal building.


The best solution to maximize energy efficiency in metal buildings is an insulation which addresses both conductive heat and radiant heat transfer efficiently.

Polyshield Triplex R21 95% reflective metal building insulation is a superior option that solves both the conductive and emissive challenges that metal buildings can present.

When following the manufacturer’s install methods, Polyshield Triplex MBI-R21 metal building insulation can provide R21 and 95% reflectivity as an economical solution.

The most common fiberglass install method is to install 3” of fiberglass under the metal roof with a plastic vapor barrier holding up the fiberglass. The 3” of trapped air that the fiberglass traps is what provides the R-value of 3.2 R-Values per inch – not the fiberglass itself.

When installing Polyshield Triplex with the same 3” of trapped air, an R-21 is achieved, while also achieving an additional 95% reflectivity.

2 thoughts on “What is the Best Insulation to Put in a Metal Building?”

  1. נערות ליווי

    Itís hard to find knowledgeable people for this topic, but you seem like you know what youíre talking about! Thanks

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