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An Introduction to Radiant Barrier Foil Insulation

It can be hard to wrap your head around how a thin sheet of reflective material resembling kitchen foil can make a such a big difference in blocking heat transfer, but radiant barrier works.

We explain all of the technical details of how radiant barrier works on our physics of foil page. This post is intended to summarize and explain the science behind radiant barrier in a simple, easy to understand way.

To understand how radiant barrier works, you first need to understand the three different types of heat transfer: conduction, convection, and radiation.

Conduction is the direct heat flow through a solid object like a wall or ceiling. Convection is heat movement through air, occurring when air is warmed. The warm air expands becoming less dense, and rises.

Radiant heat transfer is the movement of heat rays across air spaces from one warm object to another cooler object. The heat you feel from a campfire is radiant heat. This is the most dominant form of heat transfer.

Technology shows us that different types of heat contribute to the transfer of heat into and out of your home, but radiant heat accounts for the largest percentage of heat loss or gain, no matter the climate or season, making it by far the most dominant contributor.

Traditional forms of insulation like fiberglass, cellulose and foam only work to absorb and slow down conductive and convective heat. They absorb heat much the same way that a sponge absorbs water. But just as a sponge filled with water can no longer hold any more water, with every new drop that hits it, another drips out the other side. Insulation works the same way. As it becomes saturated with heat and can’t hold anymore, the insulation becomes inefficient. A single sheet of radiant barrier, on the other hand, reflects the radiant or infrared heatwaves instead of absorbing them the way other insulation does. Our radiant barrier products reflect 95% of radiant heat. That’s why radiant barrier is called a barrier, because it simply blocks the heat.

The reason radiant barrier is so effective at blocking radiant heat because it has a very low emissivity rate. Emissivity is the ability of a material to emit radiant energy. Most common building materials — brick, stone, wood, etc. – have very high emissivity rates, and in turn, they absorb large amounts of radiant energy and emit 80% to 90% of this energy to the spaces around them. Radiant barrier foil insulation, because it has a very low emissivity rate of 3% to 5%, absorbs and emits a very small amount of energy. More simply put, radiant heat passes through these objects at a much higher rate than a radiant barrier.

Here is a table comparing the emissivity rates of common building materials to that of radiant barrier foil insulation.

MaterialEmissivity
Wood
95%
Glass94%
Brick (common red)93%
Concrete92%
Steel45%
Radiant Barrier (Aluminum)3-5%


Also, radiant barrier insulation will never need to be replaced. It is made up of coated aluminum, so it will never breakdown due to UV or corrosion. Other insulation relies on their mass to remain effective, meaning that as they settle and flatten, they become much less efficient and need to be replaced. Radiant barrier doesn’t settle or flatten the way other insulation can, and doesn’t rely on thickness or mass to work. Radiant barrier can provide a lifetime of energy saving benefits.

Here is a summary of some of the other benefits that radiant barrier can provide:

  • Reduces your heating and cooling costs
  • Easy and inexpensive to install
  • Pays for itself
  • Makes you money with continued savings
  • Maintains comfortable temperature
  • Conserves valuable energy
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