What Is the Best Insulation for Exterior Walls?

Wall insulation is an essential component of every cozy home. It helps you set an ambient temperature inside your home with the minimal use of heating and cooling devices that can drive up your energy bills.

Wall insulation can prevent the entry of cold air, regulate and insulate your home from the extreme weather you may have outside, and help you to create comfortable rooms with walls that are unaffected by moisture.

An important factor of every wall insulation project is the insulation for exterior walls. Even if you’re building a new home, refurbishing your old one, or maybe the earlier insulation doesn’t do much, you must choose carefully from the existing exterior wall insulation options.

In this article, we will explore some of the best exterior wall insulations available in the market and carefully analyze each of them in terms of performance, value for money, etc.

We will also be looking at the advantages and disadvantages of each of them so that our readers can make an informed decision while considering options for exterior wall insulation.

Best Exterior Wall Insulation

Best Exterior Wall Insulation

We can’t pinpoint a single best exterior wall insulation because there are a lot of factors that can vary according to the requirements and expectations of the user.

Some might be interested in the best wall insulation money can buy, whereas others might look for a cheap exterior insulation option. Some options excel at energy efficiency, and some might leave a good amount of carbon footprint.

Let’s look at some of the best exterior insulation options for walls.

Fiberglass Insulation

Fiberglass Insulation

Fiberglass insulation is one of the most extensively used insulation worldwide. However, keep in mind that the installation of fiberglass insulation on existing walls requires the replacement of existing drywalls.

Fiberglass insulation consists of glass fibers made into batts or rolls after processing. They are excellent insulators and can prevent the spread of hot air and cold air, and even sound. It is very efficient in maintaining ambient temperature, even while allowing air in and out of the home.

Another factor that makes fiberglass insulation an attractive option is that it is very cheap and can be installed without professional help.

Fiberglass insulation has its downsides. Fiberglass insulation tends to sag over the years and can shift, causing inefficiencies in the insulation system installed.

Foam Board Insulation

Foam Board Insulation

Foam board insulation is one of the best insulation for walls in terms of insulation properties. The foam board insulation installation also requires tearing down the existing drywall and reinstalling.

Foam boards are available in the market in rigid panels made of polymers such as polyisocyanate, polystyrene or polyurethane, etc. These panels are available in various sizes and thicknesses and can be chosen according to the level of insulation desired by the client and the budget of the insulation project.

An advantage foam board insulation has over fiberglass insulation is that foam board insulation is a one-time investment. There is no need to replace foam board insulation after installation.

It is to be noted that the efficiency of foam board insulation largely depends on the installation process. Special care is to be taken to ensure no gaps are present along the seam of the boards to prevent air leakage.

Spray Foam Insulation

Spray Foam Insulation

Creating wall insulation and creating an air seal are different things altogether, even though they go hand-in-hand sometimes. If your main aim is to create an air seal for your home, spray foam insulation should be among your top picks. It will help you create a constant temperature inside your home, whether it be snowing or hot outside.

Spray foam is an environment-friendly insulation used on open wall cavities. According to the manufacturer, spray foam can be mixed with water or a special chemical reagent to be used on residential projects.

The spray foam begins to expand (the rate of expansion and the final volume after expansion depends on the manufacturer and the product used) and fills the cavity before settling down. For better efficiency, closed-cell spray foam is preferred for exposed walls.

Blown-In Cellulose Insulation

Blown-In Cellulose Insulation

It is not mandatory to tear down the existing drywall to insulate your home, and some solutions focus on this area. Blown-in cellulose insulation is one of the best insulation when it comes to refurbishing your home. Blown-in insulation can be installed even from outside your home without ever having to tear down the wall.

The installer can drill a hole inside and use a blowing machine to fill the cavity with insulation material. Cellulose is a mixture of recycled materials like newspaper and denim and hence is an eco-friendly option to consider.

Since blown-in insulation is available in a loose format, blown-in insulation can be filled according to the user’s requirement and the total budget allocated to the project.

A downside to blown-in cellulose insulation is that it can get messy during installation, especially if the loose cellulose gets inside vents and outlets. It can reach other rooms through these vents and thus require an expert for installing blown-in cellulose insulation.

Cellulose can also settle over time and shift, causing gaps and inefficiencies in the insulation system. They can lose their insulation properties if exposed to water. Blown-in insulation is quite costly compared to conventional methods such as fiberglass insulation.

Injection Foam Insulation

Injection foam insulation is somewhat similar to blown-in cellulose insulation in principle and installation mode. Injection foam is mixed with a foaming agent and water and is injected inside the cavity of a wall. Since it is foamy, it can easily fill in hard-to-reach places and provide amazing insulating efficiency.

Injection foam insulation can also create an air seal for your exterior walls, completely blocking the passage of air through the wall, thereby maintaining and regulating the inside temperature without much help from air conditioners and heaters.

Injection foam is an energy-friendly and eco-friendly solution. Injection foam doesn’t need to be maintained or replaced over time and can be considered as a long-term solution and a one-time investment.

Nu-Wool Insulation

Nu-Wool Insulation is a cellulose derivative that can provide superior insulation properties. Nu-wool can also be applied and installed in wet and batt forms. Nu-wool insulation is mostly used in fresh construction projects or refurbishing projects. It is available in both batts and rolls.

The batts consist of 70 percent recycled material, and the rest consists of renewable and natural fibers. The rolls or batts can be installed so that they can create a tight fit inside the wall insulating it from the external temperature.

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What Is a Good R Value for Exterior Walls?

R-value is one of the most important metrics to consider while choosing an insulation solution. The R-value measures the ability of a material to slow or prevent the transfer of heat under specified test conditions. An insulating material with a higher R-value is better.

It is common sense that while choosing exterior wall insulation, one will choose an insulation option with the highest R-value. But it’s not as simple as that, and R-values are dependent on different factors, such as the method and efficiency during installation.

Most insulations can be easy enough to install for the DIYers, but there are some solutions, such as the blown-in insulation, which requires a professional set of hands to install.

Moreover, the R-value is directly correlated to the cost of installation. The materials of higher R-values are created specifically for such processing and can thus cost more than other solutions such as fiberglass.

R-values are also dependent on the number of layers of blankets you use for insulation. So, for the same insulation material, if you choose to use more than 1 layer, the R-value of the insulation changes, but so does the project’s total budget.

From above, it is clear that one must compromise between factors such as R-value, cost, etc., to choose the best insulation solution for you according to your requirements.

Let us look at the R-values of standard insulation solutions to put them into perspective.


R-value per inch

Closed Cell Spray Foam


Foam Board


Open Cell Spray Foam


Cellulose Loose-fill


Fiberglass (Batts)


Fiberglass (Loose-fill)


The R-value required for an exterior wall is actually up to the homeowner and depends on the level of insulation one requires for their home. But, in some states and cities, rules and norms exist regarding the minimum R-value exterior and interior walls must-have.

Generally, exterior walls having R-value from 13 to 23 are considered appropriate.

How Does Location Affect Your Exterior Wall Insulation Needs?

We have already stated that insulating exterior walls can help regulate temperature and maintain ambiance in one’s home. But, it is only logical that the level of insulation required by exterior walls should change according to the area, its climate and building norms issued by the respective government.

The US Department of Energy(DOE) has divided the entire landmass into 8 different climate zones and are further classified based on moisture, humidity, etc. The building codes can vary according to the climate zones, and in each zona, the DOE has specified minimum R-values for insulation solutions.

It is always good to choose an insulation solution that can provide a higher R-value than the specified value to withstand sudden climate changes.

The International Code Council (ICC) has also issued an International Energy Conservation Code (IECC) that is considered the standard for efficient residential constructions.

These include specified R-values for ceilings, floors, wood, mass walls, etc. The R-values they specified are minimum, and it is always recommended to choose a higher R-value.

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Final Words

So, we have presented all the relevant facts about choosing an exterior wall insulation solution. To answer the question, which is the best insulation for exterior walls, it depends on your expectations from the insulation project and the amount of money you are ready to invest.

We have explored some of the best insulation solutions available in the market, and we have seen that all insulation solutions have their advantages and disadvantages.

If you’re thinking of creating an air seal for your home to regulate temperature, it is better to choose closed-cell spray foam or injection foam insulation. If your primary concern is to insulate the exterior walls economically, fiberglass solutions are your best bet.

We have also discussed the R-value and concluded that the desired R-value of the client is a driving factor of the cost of insulation. In many cities, there are specified norms about the required R-values, but in most places, it is upto the requirement of the user to decide what level of insulation they require.

The R-value of a material is an important metric to consider, but it shouldn’t be the only one in focus. There are many other factors to consider as each home is a fresh project and should be approached as one.

Insulating the exterior walls of your home is an important decision to make, and correct installation of the appropriate solution will grant you comfort, ambiance and peace in your home.

It is always good to consult an experienced professional to analyze your home and suggest the best insulation method.

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