Foil Insulation vs Fiberglass

Fiberglass insulation installed in a wall

Fiberglass insulation has been the undisputed standard for buildings for many years, but foil insulation is the new contender. Fiberglass has been in use by builders since the later portions of the 1800's. Fiberglass insulation comes in larger batted rolls, but is also found as a blow insulation that is primarily used in attics.

The effectiveness of fiberglass insulation is attributed to its thickness and a resemblance to a blanket. Foil insulation is typically in sheets, but can exist as foil that can be wrapped freely around most any pipe, joist or duct work. There are 3 ways that heat is transferred: conductive, radiant and convective. It is the job of foil insulation and fiberglass insulation to stop heat from escaping. The following article will help to explain the differences between foil insulation and fiberglass insulation.

The R-Factor

When you look at fiberglass insulation you will notice that they have on the packaging something called the R-value. This measures how much the fiberglass insulation transfers heat for each inch of the material being used. R-value does not measure radiant heat, which is the main way heat is transferred. This makes the R-value a disputed measurement.

Radiant heat is heat that is in the air and foil insulation can block up to 97% of radiant heat. Radiant heat makes up about 75% of the total loss or gain of heat in a building. Fiberglass and other insulating materials are great at reducing convection and conduction heat, but not radiant heat. This type of heat is either absorbed or reflected. Foil insulation is produced from aluminum which reflects heat.

Fiberglass Insulation

Even though fiberglass insulation is used the entire world over and is the standard, it is not the best insulation you can have and there are many cons. For example, look on the warning label of fiberglass material. Everyone knows that fiberglass is scratchy, but not many know the full extent of its hazards to your health. When you use fiberglass insulation you should do so with caution as breathing in the fibers can cause serious lung damage. Fiberglass insulation is made from cheap recycled materials like limestone and glass. Fiberglass insulation should also not be used in areas of high humidity because it is very susceptible to mold. Vapor barriers must always be used when using fiberglass insulation.

The cons include that it's dangerous to lungs and skin, an additional vapor barrier required, it’s useless against radiant heat, less effective over time, susceptible to humidity and dampness, fiberglass insulation acts like a sponge, absorbing water, and a potential for dangerous mold growth.

It does have some advantages though, including that it’s inexpensive, easy to install, readily available, and perfect for conduction and convection heat.

Foil Insulation

foil insulation

Foil insulation is 97% effective in blocking radiant heat and it also forms a vapor barrier and thermal break. Foil insulation, unlike fiberglass insulation, reflects heat. This means the heat from the sun does not get mixed in with cool air. The reverse is also true for the winter.

The cons include the fact that it’s more expensive than fiberglass, can be somewhat awkward to handle, and is not always available.

There are many pros, including that it’s lightweight, strong, can be used with other insulation, resists humidity and moisture, works as a vapor barrier, doesn't lose effectiveness, is easier and faster to install than fiberglass, is completely safe, and offers a radon barrier.