What is the R-Value (or R-Rating) of WareHouseFoil™ Insulation?
R-Value is a term to describe how well an insulating material resists heat flow. The higher the R-value, the greater the insulating power. In a non-conditioned area, you’ll generally have at least 2 kinds of heat: conductive heat and radiant heat. Conductive heat is described as heat that passes through a solid object (or several objects that are in contact with one another – like the layers of your roof). Radiant heat is heat that passes through a gas or a vacuum (air), so this is the kind of heat the sun gives off toward earth until it is absorbed or reflected.
This will probably surprise you but radiant barrier on its own has no R-Value!
This is important to understand because radiant barrier does not take the place of traditional insulation (fiberglass, cellulose, etc.). Traditional insulation has R-value; this works to slow conductive heat. Radiant barriers reflect radiant heat; both conductive and radiant heat are trying to enter your building on a hot, summer day (or leave on a winter day when you are running the heat inside).
The sun heats up the roof and then the heat is transferred by radiant heat across the attic space until it hits the insulation. Then, the heat transfer method switches from radiant heat to conductive heat to move through the attic insulation and into your building. This is why you need BOTH types of insulation. Traditional insulation and radiant barrier work together and each do their part. Radiant barrier is your first line of defense (against radiant heat) and traditional insulation (fiberglass or cellulose) is the second line of defense against conductive heat gain.
The sun heats up the roof and then the heat is transferred by radiant heat across the attic space until it hits the attic insulation. Then, the heat transfer method switches from radiant heat to conductive heat to move through the attic insulation and into your home. This is why you need BOTH types of insulation. Traditional attic insulation and radiant barrier work together and each do their part. Radiant barrier is your first line of defense (against radiant heat) and traditional attic insulation (fiberglass or cellulose) is the second line of defense against conductive heat gain.
What about R-Value and Bubble/Fiberglass/Foam Insulation?
Bubble foil does offer some R-Value because of the bubbles (because remember, radiant barrier does not have an R-value on its own). However, we see claims of up to R-14 for some bubble products.
If you read the fine print, this rating is always achieved as part of an overall assembly, which usually includes a lot of dead air spaces. In a lab you might be able to create a perfectly tight seal on bubble foil, but in the real world it is virtually impossible to get these results. Learn more here: WareHouseFoil™ vs Bubble Foil and other radiant barrier products.
Besides, if there is air flow around an object, the R-Value does not really matter. For example, if you have a heavy jacket and you unzip it and let air get between you and the jacket then it does not matter how thick the jacket is because you have no dead air space. So unless you can completely air-seal the bubble foil you will not get the full effectiveness of the R-value and you will be investing a lot more for no supplementary benefit.
Using Bubble Insulation
If you are installing Bubble Foil in a vented attic (meaning the attic is not sealed air tight), then you’re using it wrong. In a vented space, you don’t need bubble foil, all you need is a foil radiant barrier. You will pay extra for the bubble foil, but you will not get any additional benefit from it.
Would a 2″ inch thick umbrella keep you any cooler on a hot sunny day than a regular umbrella? The answer is no. The thickness of the umbrella is irrelevant because the air temperature is the same on either side of the umbrella. This is the perfect example of why when we are building a home or structure, we do not put insulation/radiant barrier on the interior walls between rooms. We usually only insulate EXTERIOR walls since there is a big temperature difference between the inside and the outside of the structure.
Bottom line: Radiant Barrier does not have any R-value. If you’re using it on a non-conditioned space, there is not really any reason to add traditional r-value. If you’re using radiant barrier in a conditioned space, then you want to combine the foil (with the proper air gaps) and the r-value to get the best results overall on the areas you’re heating/cooling.