Ultimate Guide to Spray Foam Insulation

Home | Articles | Ultimate Guide to Spray Foam Insulation

Spray foam insulation, or PUR foam, has become an increasingly popular choice for residential and commercial users who value the superior insulation material’s airtight performance and durability. Used in almost any project requiring insulation, spray foam is versatile, durable and airtight, which is difficult to achieve when using pre-manufactured insulation materials such as Mineral Wool or PIR Boards. Our Ultimate Guide provides insights into how and where spray foam insulation can be used in your insulation project.

What’s On This Page?

  • What Is Spray Foam Insulation
  • Why Use Spray Foam Insulation
  • Where Can Spray Foam Insulation Be Used
  • How Does Spray Foam Insulation Compare
  • Spray Foam Insulation Costs

What Is Spray Foam Insulation?

Without delving too deeply into the chemistry behind spray foam insulation, it is a two-part blend of chemicals that react with each other to create a polyurethane foam. Part A is an Isocyanate commonly found in paints, adhesives and polyurethanes. Part B comprises Polyol, which includes surfactants, fire retardants, catalysts and amines. Parts A and B are heated through a reactor, blown by air pressure to the mixing chamber and then released against the substrate as a 50:50 ratio mix.

After a second or so, the viscous liquid starts to expand and rise to its final state, usually taking up to 10 seconds. Spray foam insulation comes in two versions: a low-density Open Cell, which is very breathable and enables moisture to pass through it, whilst Closed Cell is a high-density formulation that can act as a natural vapour retarder. Both products are suitable for use in a wide range of projects; however, the type of product used will depend on the thermal requirements and the risk of moisture.

Open Cell has a thermal conductivity of 0.039 W.m.K whereas Closed Cell achieves 0.026 W.m.K. This makes Closed Cells more thermally efficient per inch of insulation installed.

Why Use Spray Foam Insulation?

There are many reasons to use spray foam insulation to insulate your building or structure, not least its ability to reduce heat loss by up to 95% and energy costs by up to 50%. The modern world is very different from the old times when energy conservation didn’t matter. Energy is expensive and predicted to continue rising over the coming years. Energy costs can vary substantially, and it only takes a shortage of raw materials, too much demand or global instability and war to change the landscape of how, where and who produces our energy. 

Then there’s carbon emissions and a global pledge to become net zero by 2050. We must reduce or control our energy consumption to live in a sustainable and environmentally friendly world. The UK has some of the leakiest buildings on the planet when it comes to heat loss. Despite more recent drives to improve insulation levels in homes, commercial and industrial buildings, we haven’t done enough. This is partly down to the type and thickness of insulation materials used historically.

There used to be a time when 100mm of mineral wool on the attic ceiling was suitable, but now the minimum standard is 270mm. Additionally, many pre-manufactured insulation materials are installed incorrectly and don’t achieve airtightness.

This is where spray foam insulation is different. It is the only insulation material manufactured in situ and spray-applied to a substrate to expand and fill every crevice where heat may escape. Its thermal performance per inch is extremely efficient compared to mineral wool insulation. This means that you may require a lower depth of insulation, which reduces the amount of space it takes up. We look at some of the core benefits of spray foam insulation below.

Airtight Performance

Pre-manufactured insulation materials like mineral wool or PIR Board require cutting to size and fitting into place before airtight tapes and fasteners are used to try and make them airtight. Conversely, spray foam insulation expands and fills every available inch within the building assembly. This creates natural airtightness of the building envelope, which slows the transfer of heat towards the exterior of the building, therefore helping occupants conserve energy.

Airtight performance has become a feature of modern construction, and spray foam’s ability to provide this in a single application helps to make it the insulation material of choice for discerning building owners.

Fast Application

Spray foam insulation can be up to ten times faster to install than pre-manufactured insulation materials. When an experienced ThermoFoam-approved operative is used, the building owner can expect several hundreds of square metres of surface area to be insulated daily. Pre-manufactured insulation materials can take several days to install because they need to be delivered to the job site, carried to the installation zone, cut to size, fit into the building assembly, secured into place, and then made airtight using tapes, fixings, and adhesives.

During the construction of newly built homes, spray foam insulation can help speed up the project. When industrial buildings or warehouses are insulated, the business’s daily operations can be impacted. In contrast, spray foam insulation can be installed in a matter of days to minimise any downtime in the business.


Have you ever checked the quality of mineral wool insulation a few years after its installation? You’ll likely find it full of dust and debris and somewhat compacted compared to its original thickness. When PIR Boards are used as an alternative to mineral wool, their lifespan will depend on the quality of fixings that hold them in place. Spray foam insulation is different because it will never shrink, degrade or reduce in performance.

It doesn’t rely on mechanical fixings and doesn’t require any ongoing top-ups or maintenance, which helps to make it the best choice for those hoping to insulate once and insulate right! Installing any insulation can be costly and disruptive to the building occupants; therefore, choosing the product that will offer maximum durability is always better. Virtually all spray foam installations are guaranteed to perform for at least 25 years.

Where Can Spray Foam Insulation Be Used?

The list is endless because spray foam insulation can be installed in the most obscure scenarios! Over the years, we’ve insulated everything from train carriages, to swimming pools, hot tubs, water tanks, grain silos and underground homes. Spray foam insulation is commonly used to insulate pitched roofs, stud walls, underfloor crawlspaces, flat roofs, shipping containers, warehouse roofs and agricultural barns. Our rule of thumb is generally, “If something needs to be insulated, spray foam will be suitable 99% of the time”. Don’t feel silly asking us to undertake a project that is out of the norm, as it is highly likely we’ll be able to help!

The only situation where spray foam is not the best solution is when installed on external roof and wall surfaces. Although it works very well as an external application, it is weather-dependent. The installation process can cause overspray droplets to travel in the air and damage nearby buildings, cars and other assets. Although protective measures can be put in place to mitigate the impacts of overspray, spray foam insulation is not always the best insulation material to be used externally.

Additionally, it reacts with UV light and degrades performance if left exposed for too long; therefore, spray foam insulation must be protected with a UV-stable coating.

Find out more about use cases for spray foam insulation by visiting our services page here: https://thermofoam.co.uk/all-services/

How Does Spray Foam Insulation Compare?

By now, you will have established that spray foam insulation is a high-performance material installed by professional contractors who process it to ensure that it provides an airtight, durable, thermally efficient, and faster result than pre-manufactured insulation materials.

That’s not to say that spray foam insulation is better than other materials, but it is important to note that many different insulation products meet certain budgets. When choosing the right insulation material for your project, it is important to research to establish which product will provide the best performance for the available budget.

If you opt for spray foam insulation for your project, you can be assured of:

  • Professionally Installed
  • Airtightness
  • Strong Thermal Performance
  • Durability 
  • Fast Installation
  • Cost Effective
  • Structural Integrity
  • Breathable
  • Natural Vapour Retarder (Closed Cell)

Spray Foam Insulation Costs

Now that you’re sold on the benefits of choosing spray foam insulation, it is important to highlight the potential costs of installing it. Firstly, it is not a DIY product; therefore, if you’re hands-on or willing and able to install your insulation, you won’t be able to do so with spray foam insulation.

In most circumstances, we’d always recommend using a professional insulation installer no matter what product or material you opt for – most insulation installers are trained and know what it takes to provide a compliant outcome that won’t damage property or reduce the thermal performance of the insulation.

When you pay a professional to install insulation, you can usually enjoy the benefits of a product warranty and workmanship guarantee, which protects you and the building if something goes wrong or the insulation damages the building.

Although most insulation materials in their raw format won’t damage buildings, property damage may occur when badly installed and items such as ventilation or vapour control layers aren’t considered. It’s always best to choose a professional.

The costs of spray foam insulation vary depending on the installation volume, the thickness required, accessibility of the installation zone and project difficulty. The more square meterage there is to insulate, the cheaper spray foam insulation becomes.

The average home retrofit installation for a pitched roof or underfloor will cost around £30-£40 per metre. For anti-condensation solutions for barns or warehouses, around 25mm of closed-cell spray foam should be used, and this will often come in at under £20 per square metre.

For new construction projects where Building Regulations need to be complied with and U-Value targets must be met, spray foam insulation can range between £20-£60 per metre. When compared to the cost of installing pre-manufactured insulation materials, spray foam insulation will likely be comparable by the time every element is considered. You can also find out more about spray foam insulation by visiting https://www.which.co.uk/reviews/insulation/article/spray-foam-insulation-ajTlp7t5K7lT

Other Guides

Spray Foam For New Build Homes

The ultimate guide to Passivhaus Insulation is designed to help those considering building to the gold standard for energy efficiency. Spray Foam Insulation can help to meet thermal targets and achieve airtightness.

Read More »

Spray Foam Insulation & Building Surveyors

In this article we look at spray foam and how it is assessed when it comes to property valuations. Building surveyors are appointed by mortgage lenders to express a detailed opinion on the property condition. The presence of spray foam is known to be a contentious issue when it comes to surveyors and lenders.

Read More »

Spray Foam Mortgage Problems – The Other Side Of the Story

In this article we look at spray foam mortgage problems that exist in the UK currently. Often, other industries and property professionals are quick to slate spray foam and refer to it as a bad product that causes damage but sometimes it’s important to listen to the other side of the story, directly from the spray foam industry.

Read More »

Ultimate Guide to Passivhaus Insulation

The ultimate guide to Passivhaus Insulation is designed to help those considering building to the gold standard for energy efficiency. Spray Foam Insulation can help to meet thermal targets and achieve airtightness.

Read More »