A homeowner touching a sheet of RetroFoam Insulation on the corner of a home's exterior

Is your home uncomfortably hot during the summer and bitterly cold in the winter? Or perhaps your heating and cooling bills are much higher than they should be.

If either of these things applies to you, your home might be poorly insulated, and improving its insulation could make your living areas much more comfortable and reduce your heating and cooling bills.

It’s not always apparent what the best solution for improving home insulation is. The design of a home influences the choice of insulation, and sometimes, there are no right or wrong answers. Very often, deciding which type of additional insulation to install comes down to budget and the level of disruption you are prepared to put up with.

Two common types of insulation are RetroFoam insulation and spray foam insulation. But what are they, and how do they compare?

They each have advantages and disadvantages, which we’ll look at in this article. So, keep reading to learn more about how these two foam insulations compare.

For more ways to save money on your heating and cooling bills, read our article on the subject here.

How Does Retro Foam Insulation Compare to Spray Foam Insulation?

RetroFoam is injected into the enclosed cavity of existing external walls of a house to provide an air seal and layer of insulation within the walls. Spray foam is designed to be sprayed onto an open surface, like the wooden sheathing behind studs, to form a layer of insulation during construction.

A man in protective gear spraying spray foam insulation on the underside of an attic ceiling.
A spray foam application in a home’s attic

So, RetroFoam and spray foam are very different products used in different ways.

What Is RetroFoam Insulation?

RetroFoam is a particular type of insulating foam made from a tripolymer-based resin. It is injected into the cavities of a house’s external walls through small holes drilled into the side of the building.

Once in place, the RetroFoam forms an airtight seal and provides a layer of insulation that helps to keep the house at a comfortable temperature, lowering your heating and cooling costs.

The foam is non-toxic, odorless, and Class A fire-rated, making it a safe and discreet way to install additional insulation in your home.

How Is RetroFoam Insulation Installed?

RetroFoam installation is a specialist job and requires a professional to ensure it is done correctly. Installation can be done from outside the house, so you don’t need to worry about moving furniture out of the way or workers walking around inside messing up your carpets with their work boots.

Neither is it necessary to rip away your drywall. Installation of RetroFoam is a very unintrusive process.

To install RetroFoam in a home, holes are drilled in the outside wall to allow access to the wall cavity. If your house has aluminum or vinyl siding, a piece will be removed halfway up the wall all around the house to allow the holes to be drilled.

The RetroFoam is then pumped into the wall via a hose inserted into the cavity. The hose is pushed to the top of the cavity first, and the top half of the wall is filled with foam, then the bottom half is filled. This way, the technician knows the hole is completely full of foam.

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

If you don’t want holes drilled on the outside of your home, the installation process can be carried out from inside your house.

Interior installation might be the preferred option if you have an old house with wooden siding that could be damaged if an attempt is made to remove it, or if you are carrying out other renovations that mean you’ll be redecorating inside anyway.

Most people prefer to have RetroFoam installed from the outside because it is less disruptive, and provided the crew takes good care, there is usually no visual evidence left behind that any work has been done. 

Benefits of RetroFoam Insulation

RetroFoam insulation is a fantastic way to improve the insulation of an existing home. Let’s look at some of the key benefits.

High R-Values

The R-value of insulation measures how well it prevents heat from moving through it, keeping cool air inside your home during summer and warm air inside during the winter.

The higher the R-value, the better the performance of the insulation. RetroFoam has a very high R-value (4.6 per inch), much higher than mineral wool, which has an R-value of just 3.14.

Fire Protection

RetroFoam is non-flammable and will help to slow the spread of fire through a building, protecting your family and home in the event of a fire.

It’s Non-Toxic

RetroFoam is non-toxic and doesn’t give off fumes or gas as it cures, making it a safe option for your family and pets.

Disadvantages of RetroFoam

Despite being an excellent option for improving the insulation of existing homes, RetroFoam does have a few drawbacks.


RetroFoam is not a cheap option. That makes it unsuitable for people on a budget, although it is possible to apply for rebates offered by energy companies, which can help to lower your cost.

Individual contractors set prices locally, so to get an idea of how much it could cost you, get in touch with a company in your area for an estimate.

Unsuitable for DIY

RetroFoam requires specialist skills, equipment, and knowledge to install correctly and shouldn’t be taken on as a DIY project. Going the DIY route on specific home improvements is a popular way to save money, but this would be ill-advised for RetroFoam.

Unsuitable For Homes Without Cavity Walls

Interior view of a wall cavity where RetroFoam has been applied on top of the fiberglass insulation
Courtesy of RetroFoam of Michigan

If your home doesn’t have cavity walls, you’re out of luck regarding installing RetroFoam. It is only suitable for filling cavities in existing walls and cannot be sprayed onto open surfaces like spray foam can, for example, in attic spaces.

If your walls don’t have cavities, you’ll need to explore other options to improve your home’s insulation.

What Is Spray Foam Insulation?

Spray foam insulation is made from polyurethane and is widely used in the construction industry as an alternative to mineral wool, fiberglass, or rigid foam board insulation. It is also used as a packaging material for protecting fragile items in transit.

The foam is made from two components (isocyanate and polyol resin) that come together as they are sprayed from a gun.

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

Closed-Cell Spray Foam

The closed-cell variety of spray foam is much stronger than open-cell and can add strength to the structure it is sprayed onto. It forms a much denser structure than open-cell foam and is a more effective form of thermal insulation, with an R-value of up to 6.7 per inch.

It is also more expensive than open-cell spray foam.

Open-Cell Spray Foam

Open-cell spray foam is cheaper than closed-cell foam but offers less good thermal insulation, with an R-value of 3.4-3.8 per inch.

As its name suggests, its structure is more open and less dense. Unfortunately, this means it is less effective as a vapor barrier and will allow moisture to move across it.

How Is Spray Foam Installed?

Spray foam is applied to open surfaces, such as the sheeting behind a stud wall or the underside of an attic roof. The foam expands to fill any gaps and provides an air seal and insulation layer that impedes the transfer of heat across it.

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.

Benefits Of Spray Foam Insulation

Spray foam insulation has some unique properties that make it particularly suited to specific applications.

Here are some of the benefits it offers:

Can Be Installed in Difficult-To-Reach Places

Thanks to the spray gun installation process and the foam expanding into gaps to fill them completely, spray foam can be applied in difficult-to-reach places more easily than other types of insulation.

Rather than spending time cutting rigid foam boards into intricate shapes, having to work around, or even temporarily removing obstacles to allow installation to take place, you can apply spray foam to difficult-to-reach surfaces with relative ease.

Excellent Insulation Performance

Spray foam, especially closed-cell spray foam, has excellent thermal insulation properties, which result in R-values of up to 6.7 per inch.

Because it expands to fill any small gaps, it forms an airtight seal, which prevents any drafts that can be a problem with other types of insulation, such as rigid foam board that is not cut precisely.

A picture of spray foam insulation covering the floor and wood studs in a wall.

Spray foam, therefore, ensures your house’s improved thermal efficiency and helps keep your HVAC running costs low.

Closed-Cell Foam Forms a Vapor Barrier

Closed-cell spray foam makes a waterproof and airtight seal around the areas it is installed, meaning you don’t need a separate vapor barrier.

Disadvantages Of Spray Foam Insulation

Despite its impressive performance and increasing popularity, spray foam does have some disadvantages.

Potential Toxicity

While there is no ruling from the EPA to suggest that spray foam is carcinogenic, concerns have been raised about the potential harm to installers during the installation process.

The company will minimize this risk if appropriate protective equipment is used, so make sure you use a reputable firm with the necessary procedures and equipment to protect its workforce and you, the householder.


Spray foam insulation is expensive to install, and like RetroFoam, you cannot install it as part of a DIY project.

The specialist kit and knowledge required to do the job well means you need to spend the money with a professional company to be sure you will reap the benefits of installing spray foam insulation in your home.


A well-insulated home will help to keep you comfortable during a cold winter or hot summer without breaking the bank on HVAC bills.

RetroFoam and spray foam insulation are widely used in the US and worldwide. Both types of foam will make your home more comfortable and lower your HVAC running costs.

The main difference for the homeowner between the two types of insulation is their installation.

RetroFoam is installed in existing external cavity walls to provide an air seal and thermal insulation. Spray foam insulation is installed on an open surface, between wall studs during construction, or between the rafters in an attic space.

To find out how much you could save by insulating your home, read our article, “How Much Does Insulation Save in Money (and Energy)?” for more information.

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