What is the Thickest Foam Board Insulation

Good insulation is important to ensure the comfort and safety of everyone at home, and part of the responsibility of building or renovating a house is choosing the best insulation. There are many available choices for insulation for many homeowners, and one of the most popular ones available is foam board insulation. We have researched information about foam board insulation and other details like thickness and quality, and this is what we discovered.

The thickest foam board insulation goes up to 6 inches thick, but needs to be custom ordered. Standard thicknesses available for most foam board insulation ranges from 1/4-inch to 2 inches, depending on the type. Obviously, the thicker the foam board insulation, the better it will be at insulating your home.

Aside from the thickness of these foam board insulations, there are other factors that you may want to consider in order to choose which ones you may need. Keep reading to learn more about foam board insulation and the best ways you can use them for your home.


External wall foam board insulation. A building contractor is installing rigid polystyrene, styrofoam insulation to the house wall and is using a spirit level, What is the Thickest Foam Board Insulation,

Types of Foam Board Insulation

There are multiple types of foam board insulation available, and they are easily available for consumers. You can choose from these types depending on the pros and cons, as well as the value of the foam board insulation you decide on.

The quality of the foam board insulation varies differently from the R-Value they offer. Below are a few of the types of foam board insulation you may see on the market.

Extruded polystyrene foam boards

Expanded Polystyrene Board  (EPS)

This type of insulation is one of the cheapest options out there. Priced at around $0.31 per square foot for 1-inch thickness, the EPS does not deplete the ozone layer and is water-resistant at higher densities. Consequently, it does have a lower R-value than other types of foam, which might be an issue depending on where you will be using it.

Extruded Polystyrene Board (XPS)

The extruded polystyrene board or XPS varies differently from its counterpart by being stronger and more water-resistant than the EPS. The downside, though, is that this particular foam board insulation includes very strong chemical flame retardants.

Also, blowing agents used on this can deplete the ozone layer. It is also priced a bit higher at $0.47 per square foot for a 1-inch thick board.

Graphite Polystyrene Board (GPS)

This particular foam board insulation may be one of the best choices out there, with graphite particles increasing the thermal performance of the insulation compared to the EPS. It also reduces the likelihood of trapping moisture by increasing its vapor permanence.

This added value also raises the cost to around $14 to $16 per board. This makes it a little bit too costly for most homeowners.

Polyiso Rigid Board (ISO)

Out of all the foam board insulation products out there, the polyiso rigid board has the highest R-value. It's also environmentally friendly as it contains no bromate flame retardant chemicals. It commonly comes foil-faced to reflect radiant heat, which makes it great for spaces needing to release heat.

With its price set at $0.60 per square foot for a 1-inch thick board, it's a great choice for homes, although, it's not suggested for below-grade applications because of its poor water resistance.

Where to Use Foam Board Insulation

Worker placing styrofoam sheet insulation to the wall at construction site

One of the key things that makes foam board insulation better than other types is its moisture-resistant quality. Another great thing about foam board insulations is that they are easy to install, as it comes in sheets or boards. It is pretty straightforward to use, and DIYers can often manage to install these insulation materials on your own.

Foam board insulation can be used in practically any location in your home that needs to be insulated. It can be used for above-grade applications like attics, ceilings, or walls.

On the other hand, below-grade applications like the basements, or other places like the interiors or exteriors of the foundation walls, foam boards prevent moisture buildups or leaks.

The applications of the insulating material for different areas of the house greatly affect the quality of energy efficiency for your home. Areas like the roof or the attic need insulating material that can deflect the heat away from the house during warmer weather while keeping the heat in during colder times. With this in mind, you may want to choose an insulating material that allows radiant heat to be reflected.

What is an R-Value?

In technical terms, the R-value is the measurement of how well a two-dimensional layer resists the conductive flow of heat. In simpler terms, it's simply the measure of the thermal resistance of the insulation material. Choosing the best kind of insulation for your home isn't solely dependent on the thickness or the type of material used, but its R-value.

One of the things worth noting is that good insulation for your home helps in saving energy. Good quality insulating materials will most likely rank higher because of their effectiveness. While it is true that installing more insulation in your homes can definitely increase the heat resistance, thicker insulation does not mean the R-value changes proportionately.

You may want to consult a local insulation contractor to see which kind of insulation would best suit your home. The R-value you need will also depend on the climate of your location, the heating and cooling systems you have in place, as well as the areas of your home you would like to have insulated.

Which Rigid Foam Insulation is Best?

There are quite a number of answers to this question and it all boils down to the need that you are trying to act upon. The insulation boards available vary in quality and pricing, and homeowners can choose which one fits their budget and where these insulating materials will be installed.

For those on a budget, a good choice for foam board insulation would be the expanded polystyrene board or the EPS. It's a great foam board insulation for most house areas that need insulation, and it can add R-value to above-grade areas like the attic or the roof.

For homeowners who face a lot of moisture-related issues in their homes, the extruded polystyrene board or XPS is one of the best choices out there. It is highly resistant to moisture without the need for special films or coating.

The pricing of this rigid foam insulation is just about the same as the EPS, and this is great for homeowners who are looking for insulation that will work for their below-grade applications on a budget.

How Long Does Foam Board Insulation Last?

Insulation of the house with polyfoam.

Foam board insulation offers firmness and water-resistance as its best qualities, which generally makes them tougher than most insulating materials used for ages. Because of these qualities, rigid boards will generally last you for about 100 years or more, provided they have been properly installed.

The durability of this product would work only if the right foam board insulation was chosen for the area it suits best. The materials used in these foam boards also make a difference in lessening replacement for your home.

Unfortunately, one of the cons of rigid foam boards is their weakness against fire resistance. This is the reason why most of the foam board insulations available on the market include some sort of fire retardant, making it not very environmentally and health-friendly to its consumers.

It is known that some chemical flame retardants can cause adverse side effects to one's health, and it is best to investigate what kind has been used for your insulating material. Because of this, do make sure to choose a foam board insulation product that includes a low-toxicity flame retardant like TCPP. Avoid polybrominated diphenyl ethers or PBDEs, and it would be best to ask a professional to help you pick the best material for your home.

In Closing

XPS polystyrene insulation boards closeup stacked on the floor

Foam board insulation comes in many thicknesses available on the market, with the thickest ones at around 6 inches made through custom order. These insulation boards vary in thickness and R-values, providing your home with the best insulation depending on the type you choose.

If you are looking for more information about insulation for your home, we have a few articles that may interest you.

How Deep Should Attic Insulation Be?

Can You Mix Different Types Of Insulation?[Esp. Blown-In]

How Long Does Insulation Last And When To Replace It

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