Reflective insulation is a radiant barrier that reflects radiant energy and heat. It has one or two reflective surfaces made of aluminum foil or aluminized polyester for extra strength.
Reflective insulation–also called foil insulation–is not an insulation product with a high R-value per inch. Its value is in its ability to reflect heat away from the building. Some foils reflect up to 95% of the heat–preventing it from transferring to the other side.
How Reflective Insulation Works
Radiation is the direct transmission of heat from a warm or hot surface to a cooler surface. Reflective insulation works in two ways. First, through heat reflectance, since heat bounces off of reflective surfaces. Radiant barriers receive ratings based on reflectance or reflectivity.
A second way this product works is through emissivity. Highly emissive surfaces are good at emitting (getting rid of) heat that accumulates on the surface.
For example, a white-painted surface is much cooler to the touch than an aluminum foil surface. They reflect about the same amount of heat, but the white surface with high emissivity can get rid of most of the heat it absorbs. Aluminum foil with low emissivity retains most of the heat it absorbs.
Reflective insulation needs to be facing an air space–usually 1” or more–to be effective. It has no value when sandwiched between two solid surfaces.
Reflective Insulation – Advantages & Disadvantages
Radiant barriers work well in some situations and not so well in others. Here are some things to take into consideration before using it as part of your building envelope.
Radiant Barrier Advantages
- Very effective in warm or hot sunny climates.
- Not affected by moisture. Radiant barriers work well in humid conditions and can double as a vapor barrier if joints are taped with reflective foil tape.
- Lightweight and easy to install as a DIY project.
- Doesn’t degrade with age.
- Non-toxic. You don’t need special equipment or safety precautions when installing reflective insulation.
- Mold free. Provides no growing medium.
- Pest free. Provides no food or nesting material.
Radiant Barrier Disadvantages
- Expensive. $0.25 – $1.00 per square foot for material and up to $1.00 per square foot for installation.
- Ineffective in cold climates unless combined with other forms of insulation. In cold climates, contractors most often use it as a wrap for polyisocyanurate rigid foam insulation.
- Must be kept dust-free for maximum effectiveness.
- An electrical hazard if in contact with live wiring.
Where to Use Reflective Insulation
- Stapled to the undersides of roof rafters in all types of buildings–houses, garages, barns, or storage buildings.
- Unventilated cavity walls.
- Recreational vehicles like motorhomes and campers.
- Close to heat-producing sources like stoves, refrigerators, etc.
Reflective Insulation Scams
Radiant barrier insulation is an excellent product in the proper situation. Unfortunately, some products with ¼” bubble wrap sandwiched between layers of foil have R-value claims of up to R-14 and exorbitant prices. The true R-value is R-1.00 to R-1.10. Reputable businesses will give you an honest assessment of your needs and whether reflective insulation will make your house more comfortable.