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Foam insulation is a type of building insulation that comes in several forms, most commonly spray foam and rigid foam boards. It offers excellent thermal resistance, making it a popular choice for both residential and commercial buildings.
Whether you are a homeowner looking to improve energy efficiency, a builder or an architect, understanding the types, properties and applications of foam insulation will help you make informed decisions about your project.
| Type | Form | Key Characteristics | Typical Uses |
|---|---|---|---|
| Open-Cell Spray Foam | Sprayed liquid that expands | Softer, less dense, better sound absorption | Wall cavities, roof spaces |
| Closed-Cell Spray Foam | Sprayed liquid that expands | Higher R-value; more resistant to water and air infiltration | Wall cavities, roof spaces, hard-to-reach areas |
| Rigid Foam Boards (EPS, XPS, PIR) | Large rigid panels | High R-value; easy to cut and fit | Walls, roofs, foundations |
The two most common types of foam insulation are spray foam and rigid foam. Other types include injection foam and structural insulated panels (SIPs). Each has its own advantages and disadvantages, making it suitable for different applications.
Spray foam insulation is a liquid foam that is sprayed into place and then expands to fill the space. It is typically used in wall cavities, roof spaces and other hard-to-reach areas, and provides a high R-value (a measure of thermal resistance).
There are two types of spray foam: open-cell and closed-cell. Open-cell spray foam is softer and less dense, making it more flexible and better at absorbing sound. Closed-cell spray foam provides a higher R-value and is more resistant to water and air infiltration.
Rigid foam insulation comes in large, rigid panels, typically used to insulate walls, roofs and foundations. It provides a high R-value and is easy to install, making it a popular choice for many construction projects.
Common types include expanded polystyrene (EPS), extruded polystyrene (XPS) and polyisocyanurate (PIR, sometimes called polyiso). Each has its own properties and typical applications. See our guides to foam sheets and foam blocks for more on rigid foam formats.
Key properties of foam insulation include thermal resistance, air sealing, moisture resistance and sound absorption. For example, if you need a high R-value, spray foam or rigid foam boards are good choices; for sound absorption, open-cell spray foam performs well. Our foam properties overview explains how cell structure affects performance.
The primary function of insulation is to resist the flow of heat. Thermal resistance is measured as an R-value, with higher values indicating greater resistance to heat flow (in the UK, insulation performance is also commonly expressed as thermal conductivity or U-values). For a given thickness, foam insulation typically provides a higher R-value than other types, such as fibreglass or cellulose.
The R-value varies with the type of foam and its density. For example, closed-cell spray foam typically has a higher R-value than open-cell spray foam, and PIR boards have a higher R-value than EPS.
Foam insulation is excellent at sealing air leaks, which can significantly improve a building’s energy efficiency by preventing heat loss in winter and heat gain in summer.
Spray foam is particularly effective, as it expands to fill gaps and cracks in hard-to-reach areas. Rigid foam boards can also provide effective air sealing when they are properly installed and sealed at the edges, for example with foam sealants or foam tapes.
Foam insulation is used in homes, commercial buildings and industrial facilities to insulate walls, roofs, foundations and more. Spray foam is often used in wall cavities and roof spaces, while rigid foam boards are often used in walls and roofs where large panels can be installed.
In homes, foam insulation can be used in walls, roofs, lofts, basements, foundations and underfloor spaces. Insulating these areas improves energy efficiency, reduces energy bills and creates a more comfortable living environment.
Spray foam is popular in homes because it can reach awkward spaces, while rigid foam boards are commonly used for foundations and basements.
In commercial buildings, foam insulation is used in walls, roofs and foundations, as well as in plant rooms, server rooms and other areas that need temperature control. This improves energy efficiency, reduces running costs and creates a more comfortable working environment.
Rigid foam boards are widely used in commercial buildings because they can be installed in large panels and provide a high R-value, while spray foam is often used for hard-to-reach areas.
Installation varies with the type of foam and the application. Spray foam is sprayed into place and expands to form a continuous layer, while rigid foam boards are cut and fitted into place. In both cases, careful installation and the correct safety precautions are essential.
Spray foam is sprayed as a liquid into the space to be insulated, where it expands to form a continuous layer. The process requires specialist equipment and should be carried out by a professional installer.
Installers must wear protective clothing and equipment to protect against exposure to the foam and its fumes, and the area must be properly prepared and ventilated for a safe, effective installation.
Rigid foam boards are cut to size and fitted into the space to be insulated, and the joints and edges are then sealed to create a continuous layer. This can be more labour-intensive than spraying foam, and it requires precision: the boards must be cut accurately and the edges sealed properly to avoid gaps. Our foam cutting guide covers the methods used.
Like any material, foam insulation has benefits and drawbacks. The main benefits are its high R-value, air-sealing ability and moisture resistance; the main drawbacks are its higher cost and the potential for off-gassing.
Foam insulation’s high R-value provides superior thermal resistance, which can improve energy efficiency, reduce energy costs and create a more comfortable living or working environment.
Its ability to seal gaps and cracks also helps prevent air infiltration, reducing heat loss in winter and heat gain in summer.
Foam insulation is typically more expensive than other types of insulation, such as fibreglass or cellulose, which can make it less affordable for some projects.
Some types of foam insulation can release gases over time (off-gassing), which can affect indoor air quality. This risk can be reduced by choosing a low-VOC (volatile organic compound) product and ensuring proper ventilation during and after installation.
Foam insulation is a versatile and effective material for insulating homes and buildings, offering a high R-value, excellent air sealing and moisture resistance. By weighing its benefits against its drawbacks, you can decide whether foam insulation is the right choice for your project.
Continue exploring foam types, formats and properties across our technical glossary:
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