Panels of blue thermal foam insulation installed over a concrete exterior wall

According to the US EPA, the average homeowner can save up to 15% on their heating and cooling bills simply by adding proper insulation and air sealing in their homes. However, the exact savings will depend on the climate zone your home is in and the level of insulation it currently enjoys.

The choice of available insulation types is enormous these days, and each one seems to have its unique benefits and disadvantages.

We’ve all heard of mineral wool, which comes in batts or rolls, and many of us are familiar with fiberglass insulation because we have it installed in our attics next to the Christmas decorations and that old set of golf clubs.

One of the least-known types of insulation is foam insulation. Unfortunately, when it comes to foam, it seems that most people haven’t even heard of it, never mind knowing what it is and its benefits.

There is a lot of confusion and misinformation around foam insulation products, and homeowners poorly understand the differences between the various types. 

This article will explain the types of thermal foam insulation available, their key features, and the situations to which each type is suited. So, to learn what’s what about foam insulation, continue reading.

What is Thermal Foam Insulation? 

Thermal foam insulation is a high-performing material made from a mixture of different chemicals derived from petroleum components. It is available in rigid sheets or can be foamed in place using small spray containers or specialist spraying equipment.

It has been around for many years and has applications in the aviation industry and home construction. However, it has become more prevalent in recent years, with solutions such as injection foam allowing homeowners to improve the insulation in their cavity walls without having to rip down drywall, which creates a lot of mess and disruption.

Thermal foam insulation comes in various types, each with distinct advantages and disadvantages.

Thermal foam insulation comes in rigid foam sheathing, made in a factory and formed into standard-sized sheets, or else is foamed in place by combining two chemical components that mix together on-site as they are applied to the building.

Several pieces of XPS foam board insulation are displayed on a table
Rigid foam board insulation

When the two components of the foamed-in-place variety mix, they react with each other and expand by 30-60 times the volume of the two original liquids.

The expansion of the foam means that it fills any small gaps and cracks in the space it is installed, which helps to form a highly effective air seal, making it a good choice for areas with irregular surfaces.

Let’s explore these various types of thermal foam insulation in greater detail.

Rigid Foam Insulation

Rigid foam insulation is made from materials such as polyisocyanate (polysio), expanded polystyrene (EPS), and extruded polystyrene (XPS).

These foams are prized for their excellent insulating properties and moisture control.

They also have fire retardants included in their design, making them a good choice for limiting the spread of fires and protecting buildings and occupants should the worst happen.

Typical R-values for rigid foam insulation range between 3.0-5.0 per inch, which is higher than mineral wool, which ranges from 3.0-3.3 per inch.

Homeowners can use rigid foam boards to insulate nearly any part of a house, including walls, roof, and even underneath poured concrete floor slabs. They are easy to work with and simple to cut into any shape or size, which is ideal for homes with bespoke features.

Foil-backed foam insulation boards have the added benefit of acting as a vapor barrier, water-resistive barrier, and air barrier, making additional components surplus to requirements and cutting down on installation costs.

Sheets of polyiso foam board insulation for use on a low ceiling

The foil face on these boards also helps to reflect heat back, which can help to direct the heat of the sun away from the house. This quality makes them perfect for use on roofs in hot, sunny areas.

Injection Foam Insulation

Injection foam is commonly marketed as “RetroFoam” or “USA Premium Injection Foam” and is a foamed-in-place product used to insulate the cavities of existing external walls.

The foam is a tri polymer-based resin mixed on-site with water and a foaming agent, producing a product that has a similar consistency to shaving foam.

To allow the foam to be injected into the wall cavity, holes are drilled into the wall at regular intervals.

In homes with vinyl or aluminum siding, a strip of siding is removed all around the building about halfway up. Holes are then drilled through the wooden sheathing into the cavity between each stud.

An installer injecting RetroFoam in the wall cavity of a home from holes in the exterior siding

A tool is inserted through each drilled hole and fed all the way up to the top of the cavity and down to the bottom to ensure there are no obstructions that could get in the way of the foam and prevent it from filling the entire hole.

Once the installer has confirmed they can access the whole cavity, a pipe is inserted through the hole and fed to the top of the opening, and the foam injection process begins. The pipe is pulled out of the cavity as the foam is pumped in.

After the top section of the cavity has been filled, the bottom section is filled following the same process. This way, the installer knows that no gaps have been left.

The injection foam is pumped into the cavity under pressure and finds its way into all the gaps in the wall, forming an air seal and insulating layer that dramatically improves the thermal efficiency of the wall.

Typical R-values for injection foam range from 4.6 to 5.0, on par with rigid foam board insulation and much better than mineral wool.

Spray Foam Insulation

Spray foam is also a foamed-in-place product, but instead of being injected into a wall cavity, it is sprayed onto an open surface, such as the wooden sheathing behind a stud wall.

The foam is formed when the two ingredients, normally isocyanate and polyol resin, mix as they are sprayed from the gun nozzle on site.

The foam coats the surface it is being installed on and rapidly expands to fill any gaps and cracks. It will typically fill the space between studs, over which installers will place drywall.

If the foam is being used in an attic space, where nobody will see it, it may be left uncovered.

A man in full protective gear is sitting on the attic floor while he sprays spray foam insulation on the underside of the attic ceiling.

Spray foam insulation has a very high R-value of up to 6.7 per inch. It is well-suited to difficult-to-reach areas where installing other types of more traditional insulation could be difficult.

It comes in two types: closed-cell and open-cell.

Closed-Cell Spray Foam Insulation

Closed-cell spray foam is denser than open-cell foam and is much more robust to boot.

Its strength allows it to be left exposed without fear of it getting damaged. It can also add some stability to the structure it applies to.

Closed-cell spray foam insulation does not allow water to penetrate, so mold and mildew cannot get a foothold.

Its waterproof properties can cause problems, though. For example, if there is a leak behind the foam, there is no way of knowing because the water remains hidden behind it. Over time, this could lead to mold, rot, and structural problems.

Closed-cell foam provides an excellent air seal and impressive insulation properties, with R-values of up to 6.7 per inch.

Open-Cell Spray Foam Insulation

Open-cell spray foam insulation is less tough than its closed-cell counterpart and can be easily ripped with bare hands. Because of this, it is usually covered over after installation, for example, with drywall.

It allows water to pass through, so you can identify leaks before they cause any rot or mold growth.

Open-cell foam makes a good air seal and has outstanding insulation performance, achieving R-values of around 3.5 per inch.

An advantage of open-cell foam insulation is that it offers good sound dampening, which is a benefit if you live in a noisy neighborhood or near a busy road with lots of traffic noise.

For a thorough comparison of the pros and cons of spray foam vs. blown-in cellulose, check out our article.

Final Thoughts: Should You Install Thermal Foam Insulation?

Thermal foam insulation is a very effective way to insulate your house because it forms a good air seal and has excellent insulation properties, with R-values significantly higher than traditional insulation materials such as mineral wool.

Injection foam is an effective and unintrusive way to improve the insulation of existing cavity walls without causing excessive disruption and mess.

Spray foam is also highly effective but is used for insulating open surfaces, such as attics or stud walls under construction. One disadvantage of spray foam is that it conceals the structure of the building, making it impossible to tell whether there is a leak behind the foam.

If a leak develops and goes unnoticed for a long time, it could cause rot in the timbers of your house, ultimately giving rise to mold and even causing structural damage.

Rigid foam board insulation is easy to work with and highly effective at insulating your home. It is a prevalent form of insulation for good reason.

Foam board won’t conceal ongoing leaks and potential rot in the same way that spray foam can, and its performance is similar, achieving R-values in the same range as foamed-in-place alternatives.

All the types of thermal foam insulation in this article are worth considering because they can save you money on your energy bills. However, given the issues that can arise from spray foam, you should carefully consider its pros and cons before you decide to use it in your home.

Further reading on insulating your home is available in our extensive archive of articles on the different types of insulation.

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