Products listed here provide insulating qualities, often through the incorporation of a radiant barrier. When they face a heat source, radiant barriers work by reflecting heat. When faced away from a heat source, radiant barriers function primarily by virtue of their low emissivityAmount of heat radiation emitted from a particular body or material. Emissivity is expressed in a fraction or ratio, with the lowest values indicating low emissivity and the highest indicating the high emissivity of flat black surfaces.. This means that the surface does not radiate heat well. A radiant-barrier surface on roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
, for example, heats up from the sunlight striking the roof, but that heat energy is not readily emitted into the attic space—so that attic remains cooler. This is why the radiant barrier seems to "reflect" heat back out of the building. An air space is required on at least one side of a radiant barrier in order for it to function as designed. Radiant barriers in attics are most beneficial in reducing cooling loads; their effectiveness in reducing heating loads is more limited. Radiant barrier products usually do not include significant recycled content, because of the lower reflectivity of recycled aluminum and the difficulty in producing very thin foils from recycled aluminum; the high embodied energyEnergy that goes into making a product; includes energy required for growth, extraction, and transportation of the raw material as well as manufacture, packaging, and transportation of the finished product. Embodied energy is often used to measure ecological cost. of virgin aluminum can be recovered through energy savings. When comparing products, look for the lowest emissivity (which corresponds to the highest reflectivity). Do not rely on "effective" or "equivalent" R-values, which are only relevant in certain climates or under certain conditions.
Products listed here provide insulating qualities, often through the incorporation of a radiant barrier. When they face a heat source, radiant barriers work by reflecting heat. When faced away from a heat source, radiant barriers function primarily by virtue of their low emissivity. This means that the surface does not radiate heat well. A radiant-barrier surface on roof sheathing, for example, heats up from the sunlight striking the roof, but that heat energy is not readily emitted into the attic space—so that attic remains cooler.
Our guide lists products from the
Greenspec® Online Directory of environmentally preferable building products. Manufacturers and/or their representatives should visit
this page to learn more about suggesting their products for inclusion.
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