What is Emissivity and Why is it Important?

The reflectivity of a radiant barrier is pretty easy to understand, the higher the reflectivity value, the more light energy(heat) the radiant barrier is able to reflect. If you look at different radiant barriers, from paints and sprayed on applications to foil rolls, you will quickly see that rolls of aluminum have much higher reflectivity values, making them more efficient than their counterparts.

But what about emissivity, why is this value so important?

Emissivity is basically the ratio of heat energy radiated by a material to the heat energy radiated by a true black body at the same temperature. Yea, I know thats a bunch of physics nonsense, so let me lay it down for you in layman’s terms. Basically, if we were to take a black object (theoretical) which reflects no light energy and absorbs all light energy that touches it, it would have an emissivity value of one (ε = 1). Any real object , weather it be black or not would have an emissivity value of less than 1.

So what this definition is really saying is that the darker an object is, the more light energy it will absorb. And subsequently, the lighter and more reflective a material is, the less light energy it will absorb. This why radiant barriers, even though they have little or no “insulative” properties, can effectively block out most of the radiant heat coming in or leaving a structure.emissivity

What is Radiant Barrier?

A radiant barrier is a highly reflective, low emissivity foil, used as a type of insulation system to permanently reduce energy costs.  Radiant barriers are ‘technically’ not an insulation material, due to the fact they are only a thin sheet of reinforced aluminum foil, however with an air space of approximately 3/4″ or more, radiant barriers have a theoretical R-value of 53. Radiant barriers affect radiant (radiation or Electromagnetic) heat transfer, the single most efficient type of heat transfer, by reflecting that radiation away from the radiant barrier. A typical home will loose heat in the winter and gain heat in the summer and the majority of that heat is radiant heat, so stopping radiant heat transfer in both the winter and summer months is the most effective way to reduce energy cost.