A question I get asked on just about all of the projects I build is, “what’s the best insulation to use?” It’s a fair question, and with more choice than ever, and a lot of it marketed as being higher performance, more sustainable, or somehow smarter than what came before, it's hard to know what is actually best.
The honest answer is that there isn’t a single “best” option. The way we build with insulation has changed massively in recent years.
It’s no longer just about thermal performance defined by a data sheet. It’s now about how materials behave in real buildings, how they’re installed, and how they’ll be durable and reliable over the life of a building.
Article continues belowWhy insulation innovations are needed
The process of specifying an insulation product looks straightforward. You meet your U- values under Part L of the building regulations, by selecting an insulation of the appropriate thickness, and then demonstrate compliance through a plethora of assessments including U-value calculations, condensation risk analysis and SAP assessments.
This process is fine on paper, but in reality, insulation performs very differently depending on the conditions it's installed in. For example, warm air carries moisture, and this moisture can move through the building fabric, through gaps, junctions and service penetrations. When it meets a cold surface, it condenses, which is where problems start.
As a result, the new generation of insulation products is starting to focus much more on buildability and issues such as moisture management, which can adversely affect an insulation's thermal performance, as well as damaging building structures.
Breathable construction methods and bio-based insulation
One of the more interesting developments has been the rise of bio-based insulation, particularly products made from hemp and recycled fibres like jute.
Insulation products such as IndiTherm and IndiBreathe Flex are starting to be used on self-build projects, especially where self-builders are concerned about sustainability. Whilst they are using eco insulation such as hemp and recycled fibres to reduce embodied carbon, the broader appeal of these products is how they deal with moisture.
Natural insulation materials such as hemp and wood fibre are hygroscopic. This means that they can absorb moisture and release it again, without deteriorating or significantly affecting their performance. Instead of trapping moisture within a wall or roof, they allow it to breathe and dissipate moisture. This doesn’t mean that a vapour control or airtightness membrane isn’t needed, but it does mean that the building structure has a better chance of drying out if something isn’t quite right.
With traditional, impermeable insulation boards such as EPS, PIR or Phenolic boards, if moisture isn’t properly managed it can get trapped. With natural fibre insulation, there’s a bit more tolerance which makes it more forgiving.
There’s also a school of thought that when a building is insulated with natural insulation, you’ll get a better internal environment. The suggestion is that homes insulated in this way feel less 'sealed', with humidity levels more stable. The result is less condensation, and a healthier internal environment that’s not affected by synthetic-based insulation products.
Alongside hemp and jute, products like Steico wood fibre boards and HempKor systems are also gaining traction. They work on similar principles – breathable, vapour open, and better at managing moisture within the building structure.
This all sounds great, but there are downsides to consider. Natural insulation products tend to require thicker build-ups to achieve the same U-values as high-performance synthetic boards. This has implications for wall thickness, architectural detailing and space.
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Improving traditional materials with bio-based binders
Not every project is suited to fully bio-based insulation, and many still rely on more conventional materials like glass wool.
What’s encouraging is that these materials are evolving. Manufacturers have started replacing traditional petrochemical binders with lignin-based alternatives which are derived from forestry by-products.
From a site perspective, nothing changes. It installs in the same way, and performs as expected. But the use of environmentally friendly binders is a step in the right direction that reduces our carbon footprint and reliance on fossil fuels.
Advances in high-performance insulation
There are still situations where you need maximum performance in minimal space. This is where high-end insulation products become essential.
Insulation products like Kingspan’s low lambda Kooltherm are widely used because they achieve very low U-values, with relatively thin build ups. In tight urban sites, or where you’re trying to maximise internal floor area, these products can become essential.
In recent years, products like Optim-R, which is a vacuum insulation panel, have pushed slimness even further. While they are eye-wateringly expensive, they are genuinely innovative, and solve problems that other insulation products can’t, such as insulating balconies where threshold details are tight.
While VIP insulation is undeniably innovative, it's not without its drawbacks. Aside from the expense, these products require careful handling, and can’t be cut or modified on site. Damage them and their performance drops significantly, which means they must be handled carefully. They’re also less forgiving in terms of moisture behaviour, so detailing and moisture management is essential.
B&Q currently stock a range of Kingspan Kooltherm insulation boards.
Robotic underfloor insulation
Suspended timber floors are a classic insulation problem area. They’re common in older homes, and insulating them properly is notoriously difficult. Access is limited, working conditions poor, and it’s very easy to miss areas. The result is cold floors, draughts, and a house that’s hard to keep warm.
Systems like Q-Bot have been developed to address this problem. Instead of sending installers under a floor, a small robot is used to apply spray insulation to the underside of the floor which would normally be difficult to reach.
The result is less disruption, a warmer floor with fewer draughts and a noticeable improvement in comfort. While this improves energy efficiency, it also reduces air movement through the floor, so careful design is needed to manage condensation risks.
What building control looks for with new insulation methods
Whilst the building regulations documents set the rules for compliance, building control officers also focus on how a building will perform in reality.
To ensure that a building is energy efficient and safe to live in, they’ll look at what insulation products have been used, and whether they’ve been installed as per the design. Key areas of focus are continuity of insulation, risk of thermal bridging and how moisture is being managed. They’ll also ask for U-values calculations and condensation risk analysis, just to make sure that the products have been properly considered and meet the required standards.
While the same rules will apply to new insulation products, as officers will be familiar with widely used standard insulation products, when it comes to newer and innovative approaches, they’ll likely need a little more convincing before signing off the approach.
Finding the right balance between old and new
For most self-builders, the challenge isn’t choosing the most advanced insulation system. It’s putting together a combination that works for the building, the construction team and still fits within the budget. This means understanding how to achieve a specific level of performance, while balancing the practicalities of installation, airtightness and moisture management.
In my experience, the best results come from a balanced approach. Using breathable materials where moisture risk is higher, high-performance boards where space is limited and always making sure that installation is carried out properly.
Insulation isn’t just about keeping heat in, it’s also about making sure that the building works – not just at completion, but for years to come.
For more in-depth advice on insulating your home, take a look at how long insulation lasts to see if this will impact your purchasing decisions, and how much insulation costs could be to help you plan your budget accordingly.
