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Useful Definitions

Useful Definitions for Understanding Radiant Barrier and Reflective Foil Insulation Products


The ratio of the radiant heat emitted by a surface. ALL materials have emissivity's ranging from 0% to 100%. The lower the emittance percentage of a material, the lower the amount of radiant heat radiated from its surface. The naturally low emissivity property of aluminum facing an air space results in very low emittance of heat from itself; it does not radiate much of its own heat from itself. This naturally low emissivity property makes aluminum ideal for use in radiant barriers.

Flame Spread:

Indicates the relative rate at which flame will spread over the surface of a material, as compared with flame spread on asbestos-cement board (rated 0) and on red oak (rated 100).

Radiant Barrier:

Per the Department of Energy (DOE), a product classified as a "radiant barrier" must have a high reflectance of 90% or more and a low emittance of 10% or less. If it doesn't reflect at least 90% of the radiant heat, it cannot be called a "radiant barrier."


The reflectivity property of reflective surface facing a heat source across an air space allowing the aluminum to REFLECT radiant heat back to the direction from which it came. Represented as a percentage.

Smoke Development:

A measurement of the obscuration of light by the combustion product stream.

Tensile Strength:

The stress at which a material breaks or permanently deforms.

Wall Plate:

Sometimes known as the top plate or ceiling plate, the wall plate is typically a 2 X 4 that is nailed along the top of the wall studs forming a wall.