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Best Overall
Sika Rmax Pro Select Polyiso Insulation Board
Getting hit with a huge utility bill is unpleasant, but it’s even worse when you know that it’s high due to heat or air conditioning loss through the doors, windows, or walls. Fitting exterior walls with insulation will reduce heat loss, which in turn should help cut utility bills. Not only can that help keep a home cozy for less, but the reduction in energy consumption is good for the environment, so it’s a win-win situation.
There’s a catch, though. While insulating walls and ceilings is a great idea, there are a number of different options to consider when it comes to insulating exterior walls, and the way the insulation is installed can vary considerably. The structure of the home and the location will also have an impact on the best choices for each application. And sadly, saving money by going green isn’t always as straightforward as we might like—especially when a contractor has to install the insulation.
To help clarify things, we analyzed some of the most popular options available, evaluating their performance and how they are fitted. While Sika Rmax Pro Select is our favorite for its versatility and ease of use, we’ve also included details on the other leading products that might be best for your situation. The result is the following guide to the best insulation for exterior walls.
Best Overall
Sika Rmax Pro Select Polyiso Insulation Board
What We Like
- Versatile; suitable for indoors and as exterior cladding
- Thinnest profile-to-R-value rating
- Lightweight and easy to use
What We Don’t Like
- More expensive than most alternatives
- Prone to damage if not handled carefully
Specs
- Type Foam Board
- Thickness 2 inches
- R-value 13.1
Sika’s Rmax Pro Select board is essentially dense foam insulation for walls in sheet form. It took this list’s top honors because it can be used indoors or out, is easy to cut and fit, and has the highest R-value per inch of any product we found. At R-13.1, the boards are only 2 inches thick (lower-value boards are even thinner), making this an ideal insulation for homes where wall space is restricted. The type of foam used here is called polyiso, which is made using pentane, an organic replacement for CFCs and thus more eco-friendly.
The boards have two faces, one white, and the other reflective, further enhancing how they can be used: They can create a barrier that restricts airflow or water intrusion, or a radiant barrier for exterior applications. In addition, the Rmax Pro boards create a continuous insulation; unlike batts or blown-in insulation, which fill cavities but don’t cover the studs, the foam boards prevent heat loss through the studs by covering them along with the cavities.
There are a few downsides to this pick, though. It is one of the more expensive types of insulation for exterior walls, and it isn’t difficult to damage, so care is needed with storage and handling.
Get the Sika insulation for exterior walls at The Home Depot.
More Insulation for Exterior Walls Worth Your Money
The following products give top-performing examples of insulation for exterior walls as boards, batts, and rolls. Our list also includes options for extruded polystyrene (XPS), fiberglass, and mineral wool, all materials that have proved to be effective over many years.
- Rockwool ComfortBatt Mineral Wool Rolls, available at The Home Depot.
- Kingspan Greenguard Foam Boards, available at Lowe’s.
- Owens Corning Fiberglass Rolls, available at The Home Depot.
- Johns Manville Fiberglass Batts, available at Lowe’s.
| Type | Thickness | R-value | |
| Sika Rmax Pro Select | Foam Board | 2 inches | R-13.1 |
| Rockwool ComfortBatt | Mineral Wool Roll | 3½ inches | R-15 |
| Kingspan Greenguard | Foam Board | 2 inches | R-10 |
| Owens Corning | Fiberglass Roll | 6¼ inches | R-19 |
| Johns Manville | Fiberglass Batts | 3½ inches | R-13 |
How We Chose the Best Insulation for Exterior Walls
Different types of insulation are suitable for exterior walls, so we considered each of them. The level of insulation that is provided for a particular thickness is important when installing indoors, but thinner products can often be more expensive, so cost can become a limiting factor. How they are fitted can differ as well: for example, some can be installed as either indoor or outdoor insulation. When putting together our top picks, we wanted to offer examples of these variations. Although our carefully collated selection features particular R-values, the same product may be available with lower or higher figures, which may be more appropriate for your particular location.
We also spoke with experienced Houston-based architect Baraa Yakzan, who agreed with the features we were focused on. She added that buyers should also consider “fire rating, if you are installing in a fire-rated wall.” She said it was important to consider “permeability/impermeability to air and vapor,” which helps solve problems with moisture and condensation. The use of a vapor barrier may or may not be warranted depending on the climate zone—it’s a complex subject, one that we also looked at in our article on faced and unfaced insulation. It’s important because, as she pointed out, if the wrong choice is made, “moisture seeps through the wall and creates mold in the insulation.”
What to Consider When Choosing Insulation for Exterior Walls
There are several key factors in finding the right installation for walls around your home, and we discuss these below. The location of the home and the climate zone will have a big impact on how much and which kind of insulation is necessary. Helpfully, the US Department of Energy has some useful information that will help you assess whether the performance of a particular product meets your needs.
Types of Insulation for Exterior Walls
Foam board is made from polyisocyanurate, polystyrene, or polyurethane and usually offers the highest level of insulation among products that can be DIY-installed. It is thinner than material that comes as batts or on rolls. It is also the only type that can be used for both interior and exterior building insulation. Foam board can be a DIY installation depending on the location within the house, but installing it after walls are in place can require significant remodeling. It’s a great addition to basements, attics, and garages as well.
Fiberglass may come as batts or rolls and is usually among the most affordable insulation for exterior walls. However, it can be quite unpleasant to work with, causing skin, eye and respiratory irritation. It can be installed by a contractor or a homeowner, but gloves, goggles, and overalls are highly recommended to avoid skin and eye irritation from the fibers.
Mineral wool, often called rock wool because it is made using rocks, comes on rolls similar to fiberglass. It is often chosen for its better soundproofing and fire resistance.
Spray foam insulation is similar to the expanding foam sold in aerosol cans. In addition to good gap filling and high R-values, it is moisture resistant. However, it is difficult to work with, so professional installation is normally suggested.
Cellulose is organic, so it’s the most environmentally-friendly choice. An excellent filler, it does a great job at preventing the passage of air. Unfortunately, this type of insulation installation has to be carried out by professionals, increasing the cost.
Any of these products could also be used for exterior garage walls, but for the door itself, we recommend a separate garage door insulation kit.
R-Values
The R-value is a way to measure the level of thermal insulation provided by a particular product. The higher the number, the more heat the insulation prevents from escaping through the ceiling or walls. However, that doesn’t mean that the exterior wall insulation with the highest R-value available is the best choice. That could be overkill, resulting in unnecessary expense without a significant benefit.
The recommended R-value of insulation varies depending on the climate zone, and charts are available online for guidance. Normally the highest R-values are suggested for insulation for the attic, which is usually where most heat loss occurs. When referring to outside wall insulation, the numbers are somewhat lower. They can still be anywhere from around R-13 to R-20 or more.
Thickness
All insulation varies in thickness depending on the R-value. Some types of insulation tend to be thicker than others. For example, if you compare foam board with fiberglass or mineral wool insulation of the same R-value, the foam board requires less thickness to provide the same R-value.
Thickness can have an impact when installing insulation for walls from the interior of the building. Fiberglass and mineral wool are popular to use between studs, but achieving the required R-value may be difficult if the chosen insulation is too thick for the depth of wall space available. With so many different insulation products on the market, there will often be thinner alternatives, and board is a common solution—but this can result in higher costs. All aspects of a particular insulation material need to be taken into account before choosing the best option.
FAQs
The article above gives specific information about the different types of products and their performance characteristics. It should help in finding the best insulation for the exterior walls of a home. But while we were researching these products, we also came across a number of more general questions, so we have answered those here.
The insulation R -value will depend on the construction of the walls and where you live. Numbers could be anywhere from R-13 to R-23. Colder climates require higher R-values. Our article on how much insulation you need provides additional information.
Thickness varies depending on the material. It’s more a question of deciding the R-value you need, then assessing the thickness of relevant products and determining whether they will fit into the wall space you have available.
Fiberglass can last for 60 years or more if properly installed. However, dampness or rodent nesting can cause the fiberglass to compress and deteriorate, reducing the lifespan. Even then, fiberglass should last for at least 30 years.
Initial costs can be high, especially if the insulation has to be installed by contractors. If it’s tackled as a DIY job, it can take considerable time and disrupt day-to-day life.
No. Fiberglass has insufficient weather resistance and is susceptible to mold and mildew, and needs to be protected by the walls of the home.
