What Insulation Has the Highest R-Value Per Inch?

Insulation is an integral part of every household, and when it comes to insulation, the “R-value” is one of the most important metrics to be considered.

It’s easy to hire someone to do the insulating for you while you relax. Still, you have to make choices that can directly affect the aesthetics, internal comfort, and overall insulation efficiency.

It’s common knowledge that some insulation materials outperform others in terms of efficiency and thermal resistance.

This article will introduce the insulation materials with the highest R-value and discuss how R-value can be used to make informed decisions regarding insulating your home.

What Insulation Has the Highest R-Value Per Inch

What Insulation Has the Highest R-Value per Inch?

To answer your question, Rigid foam panels are the insulation with the highest R-value per inch in most cases. A few factors affect it, including the manufacturer and the quality of the panel. Rigid foam panels are also known as “continuous insulation” or simply “foam board.”

As is the case of most insulations, rigid foam panels also have many varieties in the market. But, inherently, most rigid foam panels are made up of two layers of panels sandwiching a layer of expanded foam—the foam consists of pentane, or chlorofluorocarbons, as well as hydro chlorofluorocarbons. However, since the CFCs and HCFCs have adverse environmental effects, it is not promoted and recommended.

Rigid foam panels, having the highest R rating insulation, can insulate walls, ceilings, floors, foundations, etc., during the construction phase. They come in different materials, and thus the R-value of the insulation also varies for each variety.

  • Polystyrene boards can have an R-value ranging from R-3.8 to R-5.0.
  • Polyurethane boards have an R-value of R-5.5 to R-6.5.
  • However, polyisocyanurate, one of the highest-rated insulation, can have R-values ranging from 5.6 to 8.0.

R-Values of Different Types of Insulation

Simply put, R-value is a measurement used to quantify a material’s thermal resistance. There are many materials used for the thermal insulation of buildings worldwide, and we have previously seen the R-values of rigid foam boards.

To put it into perspective, let us compare the values of rigid foam boards with that of the other extensively used insulation solutions.



Foam Board


Closed Cell Spray Foam


Open Cell Spray Foam


Cellulose (Loose-fill)


Fiberglass (Batts)


Fiberglass (Loose-fill)


What does a high R-value mean?

What does a high R-value mean

As mentioned above, R-value is a dimensionless quantity used to quantify the ability of a material to resist the flow of heat through it. So, having a higher R-value is an indication that the material is a better insulator.

R-value of a material is not fixed, i.e., it can change according to many deciding factors, including quality of material used, the manufacturer of the product, the thickness of the material, etc. It can also be affected by other phenomena that can render your insulation ineffective.

An example of that is fiberglass insulation, one of the most extensively used insulation material. It has been seen that during cold weather, the R-value of fiberglass insulation drops if the temperature goes below 32 degrees. This can lead to problems inefficiency of the system. Another such factor that can affect the efficiency of insulation solutions is water.

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Is a high R-value good or bad?

Yes, a high R-value is a factor to consider while planning to insulate one’s home. But, it is not the only one. A high R-value can provide better insulation materials, but it doesn’t necessarily provide superior insulation. This is because the test for determining R-values doesn’t consider the air leakage of the material, which can decrease the R-value of the material.

Air seals should also be considered during the installation of insulation solutions. Air seals are seals that don’t allow the passage of air, vapor, moisture, etc. Creating an air seal provides you with a strategic advantage of drastically increasing the efficiency of your home’s insulation. This can prevent heat transfer and keep the conditioned air inside the home, further driving down the energy costs.

Even though having a high R-value can have a good effect on the insulation properties, it can drive up the cost of installation. High R-value materials tend to cost more, making your budget for the insulation project pretty big if you don’t select a suitable material.

What R-Value Should You Choose?

The R-value you should use for your project depends upon your end goals. If you aim for superior insulation, you can opt for high R-value materials. But, know that superior insulation doesn’t always mean highly efficient. If you aim to create an air seal to block air leakage, factors like R-values don’t account for too much.

Remember that the most efficient insulation material need not be the one with the highest R-value. It always depends on the material you choose and how it can perform under the given circumstances.

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Foam Board Insulation R Value Chart and Types
Open-Cell vs Closed-Cell Spray Foam Insulation
Batt vs Blown-In Insulation
What Is Blanket Insulation

Final Thoughts

In this article, we have seen some insulation solutions and their R-values, out of which rigid foam panels had the most R-value in terms of insulation efficiency. We have also compared rigid foam panels with close competitors to provide the user with maximum information to make an informed decision.

We have also discussed the role of R-values of the chosen material in determining the level of insulation one needs for their home. It can be concluded that although R-values are useful metrics when it comes to insulation, they shouldn’t be the only ones you look for while buying insulation.

Whether attic insulation or wall insulation, air seals are just as important as insulation ratings. It is the end goal and the requirements you should focus on rather than selecting the material with the highest R-value.

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