20th Feb 2023 -

Foam board insulation is one of many types of insulation materials available. Its versatility and density make it a popular choice for both home and workplace environments, such as allowing a wall to breathe and blocking unwanted moisture. With a wide selection of materials available to choose from, foam board insulation could prove to be the best insulation for your building project. 

What is foam board insulation?

Foam board insulation (also known as foam insulation board) is manufactured as rigid panels and is an alternative insulation choice to fibreglass batt insulation, which is mainly used in homes. This type of insulation shares some similar qualities to PIR insulation and is great for the exterior of a house under a house wrap, a building’s exterior foundation, and against the foundation in a basement.

Foam board insulation also has good R-Value numbers. The R-Value number indicates the insulation resistance to the flow of heat, as well as its thickness, material and density. For example, if the R-Value is high, the insulation material resists the heat flow well and is of good quality. Depending on the type of foam insulation board, the R-Value ranges from 3.6 per inch to 8.0. 

There are 4 different types of foam board insulation to know about.

1. Polyiso (Polyisocyanurate)

This is a very dense foam board insulation. It provides an R-value of 7.0 - 8.0 per inch of thickness and often comes foil-faced to help reflect radiant heat. Polyiso comes in several thicknesses and is used over house sheathing underneath siding or in attic spaces where its reflective properties are very effective.

2. Polyurethane

Known primarily for its sound-insulating qualities, polyurethane is manufactured in different variations such as sheet insulation and board insulation. Polyurethane can also come as spray foam, which is particularly useful for insulating areas where boards and sheets are not permitted, such as tight corners. Its R-Value ranges from 3.5 per inch of thickness for open-cell spray foam. For closed-cell spray foam, the R-Value is 6.0 per inch of thickness. 

3. Expanded Polystyrene (EPS)

This is the same material as what a takeaway box or disposable coffee cup is made from. It is primarily used to protect fragile items in their packaging. It provides an R-value of 3.6 - 4.0 per inch of thickness and is considered to be the cheapest type of foam board insulation. EPS is used under roofing, over the foundation walls and beneath the siding.

4. Extruded Polystyrene

Extruded Polystyrene insulation is the rigid pink or blue panels that can be found at home centres in many different thicknesses. It is denser than EPS and provides more R-Value with a rating of 4.5 - 5.0 per inch of thickness. This insulation is available with straight or tongue-and-groove edges to help limit air movement. It is available in all different size configurations to accommodate lots of different applications.

Advantages of foam board insulation

Not only is foam insulating board easy to install, but it is effective across a wide range of applications, whether you use it for a ceiling, wall or floor. Here are the main advantages of foam board insulation to consider.


Resistance to moisture varies between foam board insulation types. However, all of them can help to control moisture levels - they protect the interior framing from factors like humidity and rainfall. Plus, the insulation also keeps interior sheathing warm so moisture does not pile up. It can also stop mildew and mould from entering the material, but they can still grow on its surface. 

Stops thermal bridging

Foam board insulation prevents thermal bridging, where heat passes through more conductive materials instead of passing through the insulation. Whether it is insulation boards for walls or insulated roof sheets, thermal bridging mostly develops when interior insulation suffers a break and crosses with other materials such as studs. Construction professionals install this insulation on the exterior of the building, which prevents thermal bridging from happening. 

Air leak prevention

The insulation acts as a stable seal on the exterior of your workplace or home and helps to stop any air leaks from occurring. An air leak can happen when either too much air enters or leaves a building. If an air leak does happen, it can greatly affect energy efficiency. It can also prevent pests from entering, help with any allergies, as well as improve the overall air quality. Spray foam will particularly be useful for smaller seals and cracks. 

Disadvantages of foam board insulation 

You may have already decided to choose foam board insulation for your home or workspace after reading about all its benefits. But it is important to know about the potential downsides before you go ahead. Here are a few factors to consider.

UV light sensitivity

Although this is not an issue after installation, this insulation has proven to be sensitive to sunlight and other UV light. It is essential to store the insulation properly, away from UV light once you have bought it. If the insulation is exposed to UV light, it can become brittle and yellow discolouration can also occur. 


Unfortunately, foam board insulation can cost more to buy compared to other insulation types. This will be a higher upfront cost for insulating your home or building project, so you will need to factor this in when planning your project. However, it helps to save energy - over time, you will save on your energy bills and you would have made a firm investment for the future. 

Installation problems

You will not need to buy any special equipment when you come to the installation. But it is important to meticulously follow the installation instructions. Any mistakes could lead to significant issues, such as air penetrating the insulation. This would happen if the seams between the cavities and boards are not sealed correctly. 

How to cut foam board insulation

Generally, it is sold as a standard 4ft x 8ft size - or in smaller sizes - and the thickness of a board can range from 6.35mm (¼ inch) to 50.8mm (2 inches). Because of its material and flexibility, foam board insulation is easy to cut to the size you require. For a quick and clean cut, you can either use a utility knife or a circular saw for thicker boards. With a tape measure, size up the dimensions you need and mark them out on the foil backing. Then you will cut along the marked line - for any corners and curves, a jigsaw will do the trick. Be sure to wear safety goggles and use a sturdy workbench. 

How to install foam board insulation

Once the insulation is cut to the desired size, you can learn how to attach rigid foam board insulation between studs. Luckily, both are fairly simple to do. If you are using the insulation between studs, you simply place it in the slot areas. Each board should fit comfortably, so not too tight that the foam begins to tear. If this does happen, take the board out and trim it down slightly with a saw. To seal the gaps, use a low-expanding spray foam sealant. 

Does foam board insulation need to be replaced?

The lifespan depends on the type. Over time, the insulation can lose its R-Value due to several factors, such as general wear and tear, water damage, fire damage and being exposed to pests. Below summarises the estimated lifespan for all 4 types of foam insulation board.

Insulation typeLifespan
Polyiso (Polyisocyanurate)15 - 20 years
Polyurethane50 years
Expanded Polystyrene (EPS)30 - 50 years
Extruded Polystyrene15 - 50 years

Can you paint over foam board insulation?

As well as spray foam insulation, you can paint over it if for any reason you are not able to cover it with drywall. But before you choose a colour scheme, there are a few steps you should follow. 

1. Sanding - With a bit of sandpaper, be sure to sand down the edges of the insulation. It will help you to achieve a smooth finish - you should wear a face mask to protect yourself when doing this.

2. Painting - It is suggested that two or three coats of paint should provide enough coverage. Multiple coats will allow the paint to properly fill the pores of the foam. If you are using a spray gun, make sure to not hold it too close to the wall insulation board - this will cause the paint to drip and run down the surface. 

3. Waxing - After the paint has completely dried, use a wax sealant over the surface. This will add protection for the paint. 

Can you put batt insulation with foam board insulation?

Some have made the comparison of batt insulation vs foam board insulation. But both types of insulation can complement one another. Using both together will increase the insulation’s R-Value and add an additional moisture barrier to your home or building project. You can use rigid foam board insulation with many other types of insulation, except mineral wool. This is because foam board is flammable and mineral wool is fire-resistant. The combination of batt and foam board insulation is commonly used for areas such as exterior walls, bathrooms, basements and ceilings. 

Great competitive trade prices for foam board insulation

Building Materials Nationwide is your one-stop shop for all the thermal and acoustic insulation products you need. Whether you want insulation boards for your walls or a roof insulation board for your project, we are able to help you buy the best products with quick delivery options. 

If you are a building and construction professional, you are welcome to open a trade account with us. You have the option to open a cash or flexible credit account, which can help to ease any pressure of paying for your tools and materials upfront. Also, when you sign up, you will benefit from your own knowledgeable account manager who can organise every order and delivery for you. Find out more by giving us a call or signing up straight on our website.