The 5 Best Cavity Wall Insulation Options for Your Home 2023 Written by Sophie Lewis Updated on 3 August 2023 ✔ Cavity wall insulation materials range in price from £5-£75 per square metre✔ Mineral wool is the best option for older properties✔ Rigid insulation boards or cavity batts are the best option for newer propertiesThere are many ways to insulate your property's cavity walls (check out the costs of spray foam insulation, for instance), but some ways are better than others.After all, about a third of all the heat lost in a home escapes through the walls (Energy Saving Trust, 2023). By properly insulating cavity walls, you can save energy and cut costs off your heating bill. In this article, we share the best cavity wall insulation options to consider for your home.If you’re considering spray foam insulation, you can find the best deals by simply popping a few details in this quick form. Once we have these, we’ll put you in touch with our trusted insulation installers, who will provide you with their top deals. What's on this page? 01 What are the best types of cavity wall insulation? 02 Is cavity wall insulation right for your home? 03 Which type of cavity wall insulation should you get? 04 The best type of cavity wall insulation for older properties 05 The best type of cavity wall insulation for newer properties 06 FAQs What are the best types of cavity wall insulation?The suitability of each cavity wall insulation type depends on various factors such as the construction of your home, the climate in your area, and your budget. Here are some of the most commonly used:Spray foam insulation – a mixture of polyol resin and isocyanate that create a foam, which is sprayed into cavity walls and expands to fit the space and form a sealMineral wool – made from natural or synthetic fibres derived from minerals such as rock or glassBeads and granules – small foam particles typically made of expanded polystyrene (EPS)Rigid insulation boards – panels typically made from expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate (PIR)Cavity batts – mineral wool that has been compressed to form slabs, covered with a water-resistant filmSpray foam insulationSpray foam insulation is applied using a spray application method. It consists of a mixture of two components, polyol resin and isocyanate, which react and expand upon contact to form a foam.It’s available in two types: open-cell foam and closed-cell foam. Open-cell foam is softer and less dense, while closed-cell foam is denser and provides a higher level of insulation. The foam is sprayed onto the designated areas, conforming to the shape of the space being insulated.The foam adheres to the surface, creating a continuous layer of insulation that effectively reduces heat loss or gain and helps to prevent moisture-related issues such as condensation.The average price of spray foam insulation is £20-£50 per square metre.The pros and cons of spray foam insulation Pros Provides a high level of thermal resistance with a long lifespan Expands upon application, creating an airtight seal, minimising air leakage and preventing drafts Closed-cell spray foam insulation is impermeable to moisture Conforms to the shape of the area being insulated, ideal for irregular or hard-to-reach spaces Cons Generally the most expensive of insulation materials Not typically a DIY project – should be installed by trained professionals Spray foam can release chemicals into the air which could cause respiratory irritation and allergic reactions Challenging to remove or modify if required Mineral woolMineral wool is an insulation material made from natural or synthetic fibres derived from minerals such as rock or glass. It works by trapping air within its fibres, which helps to reduce heat transfer.Mineral wool insulation is installed by blowing the material into the cavity using specialist equipment. The material fills the voids, providing an effective thermal barrier. It can significantly reduce heat loss through the walls, improving the energy efficiency of a building. It also offers soundproofing benefits by absorbing sound waves.The average price of mineral wool is £13-£17.50 per square metre.The pros and cons of mineral wool Pros Excellent thermal insulation Good sound-absorbing properties Moisture resistant One of the cheaper insulation materials Cons May settle or sag overtime, reducing its effectiveness Relatively dense and heavy, making it harder to install Can release airborne fibres during installation which can cause skin irritation or respiratory discomfort Beads and granulesBeads and granules insulation utilises small foam particles to fill the gaps and voids in the wall cavity. These particles are typically made of expanded polystyrene (EPS). The installation process involves drilling small holes into the external walls of the property at regular intervals.Through these holes, the foam particles are blown into the cavity using an injection system. As the particles are injected, they disperse and interlock, forming a continuous layer of insulation that fills the available space and reduces heat transfer. The drilled holes are then filled to restore the appearance of the walls.The average price of beads and granules for cavity wall insulation is £18-£22 per square metre.The pros and cons of beads and granules Pros Reduces heat transfer and improves energy efficiency Typically quick and non-disruptive installation Good flow characteristics, which helps fill cavities evenly for more consistent insulation coverage Good sound-absorbing properties Cons May settle or compact within the cavity, reducing insulation effectiveness May have limited resistance to moisture May allow some air movement that can reduce the overall performance May be more expensive compared to other cavity insulation options Rigid insulation boardsRigid insulation boards are typically made of materials such as expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate (PIR). The boards are fixed to the surface of the wall or other areas using adhesive, mechanical fixings, or a combination of both.The boards are cut to fit the required dimensions and then secured in place. Joints between the boards are sealed to ensure a continuous insulation layer. They work by reducing heat transfer through conduction. The closed-cell structure of the boards traps air, preventing the movement of heat.The cost of rigid insulation boards vary slightly depending on the material used. Typically per square metre EPS boards are around £10, PIR boards cost about £5-£15 and XPS boards are £10-£15.The pros and cons of rigid insulation boards Pros Excellent thermal resistance properties Rigid and sturdy, providing structural support Moisture-resistant, preventing the growth of mould and mildew Usually the cheapest insulation option Cons Not as flexible as other insulation materials, challenging to install in irregularly shaped or curved spaces Can allow heat to bypass the insulation with air gaps if not properly installed Improper installation can lead to moisture-related issues leading to rot or corrosion XPS and EPS are derived from petroleum-based products so not environmentally friendly Cavity battsCavity batts are typically used in new builds or extensions where the cavity width allows for full-fill insulation. The batts are slabs of mineral wool that have been compressed together and covered with a water-resistant film. The slabs are fitted tightly together to fill the entire void, reducing heat transfer through the walls.The typical cost for cavity batts ranges anywhere from £12 to £75 per square metre depending on the thickness of the batts.The pros and cons of cavity batts Pros The most fire resistant of insulation materials Lightweight and easy to install Have a water-resistant coating Made from eco-friendly materials, such as recycled or sustainable fibres Cons Can only be installed in the process of building a home, can’t be retrofitted Not as efficient at insulating compared to foam that expands or beads that fill gaps Can retain moisture, leading to dampness or condensation issues, if improperly installed Costly to install when thicker batts are required Is cavity wall insulation right for your home?The main problem with cavity wall insulation is determining whether it’s actually right for your home, which depends on various factors. Firstly it is important to ensure that your home has a cavity that is suitable for insulation. It’s unsuitable for walls where there isn’t a gap at least 50mm wide.It's essential to check your property meets the necessary building regulations and requirements for cavity wall insulation. Factors such as exposure to wind-driven rain, brickwork in bad condition, and the presence of damp or structural issues should be considered.If your home meets the requirements and has poor insulation (for example you experience issues with heat loss, cold spots, or high energy bills) then cavity wall insulation is certainly worth considering. Which type of cavity wall insulation should you get?The type of cavity wall insulation you should choose depends on various factors. These include the specific characteristics of your property, your insulation goals, budget, and any other considerations you believe important such as soundproofing or fire resistance. The best type of cavity wall insulation for older propertiesThe best type of cavity wall insulation for older properties is mineral wool. This is because older properties are often more prone to issues such as moisture and condensation. Mineral wool is breathable, allowing moisture to pass through the wall while still providing insulation. This helps in maintaining a healthy and dry environment within the property.Mineral wool also has excellent fire-resistant properties, making it a safe choice for older properties. It is non-combustible and can act as a fire barrier, reducing the risk of fire spread within the cavity walls. It also has good soundproofing properties, which can be an added benefit in older properties that may have thinner walls.As mineral wool is installed through small, drilled holes, it minimises any impact on the external appearance of the property, preserving its original aesthetics. The best type of cavity wall insulation for newer propertiesFor newer properties, one of the best types of cavity wall insulation is rigid insulation boards. They have excellent thermal insulation properties and can enhance the structural integrity of the walls as they are rigid and provide additional support.They are typically moisture-resistant too, particularly beneficial for newer properties where maintaining a dry and moisture-free cavity is important to avoid potential future issues such as damp or mould.Rigid insulation boards are straightforward to install, especially in properties with accessible cavities. This ease of installation can save time and labour costs during the installation process. For homes that aren’t built yet, cavity batts are worth considering due to their superior fire resistance.Next steps As we’ve covered in this article there’s various cavity wall insulation options available, and there isn’t a one size fits all solution. Consulting with insulation professionals or surveyors should be the first step you take as they can help evaluate the suitability of different insulation types and recommend the most appropriate solution for your home.To find the best deals for spray foam insulation, we can put you in touch with our trusted insulation installers. Simply add a few details into this quick form and they’ll get in touch directly with their best deals. FAQs What is the most efficient cavity wall insulation? The most efficient cavity wall insulation is spray foam – it expands upon application creating an airtight seal, providing a high level of thermal resistance with a long lifespan.Want to see if spray foam is right for you? Check out our guide: Is Spray Foam Insulation Worth It? What insulation should I use in a cavity wall? The type of insulation you should use in a cavity wall depends on several factors including the age and construction of your home, the climate in your area, and your budget. Older properties benefit from mineral wool which is breathable and can be installed without any obvious aesthetic changes.Newer properties may be better using rigid insulation boards that can enhance the structural integrity of the walls and are typically moisture-resistant. What houses should not have cavity wall insulation? Houses that should not have cavity wall insulation include timber-framed properties, steel-framed properties, properties experiencing issues with penetrative damp, and properties with a cavity wall under 50mm or over 150mm. Written by: Sophie Lewis Sophie is a content writer and editor who specialises in the areas of sustainability, property, and interiors. She has written content for several estate agency brands across the UK, as well as publications such as Readers Digest.