Ask the Expert: What is the difference between reflectivity and emissivity?

Published on: Jan 21 2014 by darnold

Reflective Insulation Expert answers questionsWhat is the Difference Between Reflectivity and Emissivity?

Although reflectivity and emissivity are both important indicators of insulation’s effectiveness, they are rarely explained. Understanding what reflectivity and emissivity are can help you to choose insulation for your home.

 

Reflectivity

Reflectivity refers to heat or light that bounces off of a surface and is returned to its source. Reflective insulation requires a high reflectivity to keep heat within a house in cold weather, and reflect extra sunlight in warm weather.   Pure aluminum is one the most reflective surfaces available and EcoFoil reflective insulation uses 99.9% pure aluminum to reflect 97% of radiant heat.

 

Emissivity

By contrast, emissivity is a measure of how much heat penetrates the surface and radiates through it. In general, any heat that is not reflected by a surface is emitted by it. Dark colors tend to have high emissivity. Unfortunately, many common construction materials, such as asphalt, roofing paper, and dark paints have high emissivity values.

 

To illustrate: a black roof reflects only 4% of the sunlight that hits it. This means that 96% of that sunlight is emitted as heat. The result: it can become up to 85 degrees hotter than nearby surfaces!  Fiberglass insulation takes the sun’s energy and emits 75% of the energy as radiant heat.  Compare that to reflective insulation which emits only 3% of the energy from the sun.

 

Bottom line: materials with high emissivity will radiate more heat back into the structure. This means more energy is required regulate the temperature of a home.

 

How reflective insulation products can help

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The good news is that insulating roofs and heating vents ducts with reflective insulation can help to counteract emissivity and the movement of heat. Radiant barrier and reflective insulation products like EcoFoil work by reducing the heat transfer from the underside of the roof to the living area inside.  Save money and make your home more comfortable by adding EcoFoil to your home, workshop, or metal building.

 

For more information on the science of heat transfer and insulating your attic with EcoFoil products, visit our reflective attic insulation page, or give us a call at (888) 349-3645.

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