When it comes to home energy efficiency, few upgrades offer the long-term benefits of quality wall insulation. As concerns over rising energy costs and environmental sustainability continue to grow, proper insulation has moved from a construction afterthought to a top priority. To assess just how well different types of wall insulation perform under various conditions, we conducted an in-depth performance test in a controlled environment. What we found may influence how you think Air Source Heat Pump in london about insulation in your own home or building project.
Why Wall Insulation Matters
Before diving into our findings, it’s important to understand the role wall insulation plays. Essentially, insulation slows the transfer of heat between the inside and outside of a building. In cold months, it keeps warm air in; in hot months, it keeps cool air from escaping. This not only enhances comfort but also reduces heating and cooling costs and minimizes the building's carbon footprint.
Our Testing Approach
We designed a comparative test to evaluate four commonly used insulation Solar Panel Installation london materials: fiberglass batts, spray foam, cellulose, and rigid foam board. Each material was installed in identical 4 ft. x 4 ft. wall assemblies built with standard 2x4 wood framing and drywall. All panels were exposed to identical temperature differentials, humidity levels, and air movement to simulate real-world conditions. We monitored thermal resistance (R-value), air leakage, moisture absorption, and overall durability over a six-week period.
Fiberglass Batts
Fiberglass insulation is one of the most widely used and cost-effective materials. It’s made of fine glass fibers and typically comes in rolls or batts. Our tests showed that fiberglass performed reasonably well in moderate conditions, maintaining an R-value around R-13 for a 3.5-inch wall cavity. However, it lost some of its effectiveness when exposed to high humidity.
One major downside was its vulnerability to air leakage. Even with a precise installation, small gaps between batts and studs allowed air to pass through, reducing overall thermal performance. Moreover, if fiberglass gets wet, it compresses and loses insulating properties permanently, making it less ideal for climates with high moisture exposure.
Verdict: Inexpensive and decent performance in dry conditions, but poor warm home grant air sealing and moisture sensitivity are drawbacks.
Spray Foam Insulation
Spray foam performed the best in terms of R-value per inch and air sealing. We used closed-cell spray foam, which expands on application and hardens to form a solid, air-tight barrier. The initial R-value reached as high as R-6.5 per inch, allowing us to exceed R-20 in the same wall cavity space.
Its airtight seal was unmatched. In blower door tests, the spray foam panel had virtually no air leakage, a key factor in maintaining a consistent indoor climate and reducing HVAC loads. Additionally, spray foam was resistant to moisture and added structural rigidity to the wall cavity.
However, it is also the most expensive option and requires professional installation, which can add to the cost. There are also environmental considerations, as some spray foams contain chemicals with high global warming potential.
Verdict: Superior thermal and air sealing performance, ideal for energy-conscious homeowners willing to invest more upfront.
Cellulose Insulation
Cellulose is a recycled product, often made from shredded newspaper treated with fire-retardant chemicals. It’s typically blown into wall cavities and has a competitive R-value of around R-3.6 per inch. In our test, cellulose demonstrated solid thermal resistance and surprisingly good air sealing, especially when densely packed.
One of the advantages of cellulose was its ability to fill irregular cavities more effectively than fiberglass batts. It also scored well in sustainability, being made from up to 85% recycled material. Moisture resistance was moderate — better than fiberglass but not as good as spray foam. In high-humidity conditions, it retained some moisture but dried out without significant degradation.
On the downside, installation requires special equipment, and settling can reduce effectiveness over time if not properly installed.
Verdict: A great eco-friendly option with strong performance, though settling and moisture must be managed.
Rigid Foam Board
Rigid foam boards, typically made of polystyrene or polyisocyanurate, provide a solid barrier with a high R-value per inch (R-5 to R-6.5). These boards were easy to install in our test panels and provided excellent thermal performance when properly sealed at the joints with tape or spray foam.
Where rigid foam stood out was in moisture resistance — it simply does not absorb water. However, its performance heavily depends on proper installation. Any gaps between the boards and framing can lead to air leakage. It’s also bulkier and harder to retrofit into existing wall cavities unless the wall is open.
Durability-wise, rigid foam held up well over time and maintained consistent R-values throughout the testing period.
Verdict: Excellent thermal and moisture resistance with good durability, but installation must be meticulous to avoid air leaks.
Final Thoughts: What We Learned
After six weeks of detailed testing, our findings confirm that not all insulation Electric Storage Heating in london is created equal — and performance depends not just on the material itself, but on how it's installed and the conditions it's exposed to.
Best Overall Performer: Spray foam, for its superior R-value, air sealing, and moisture resistance.
Best Eco-Friendly Option: Cellulose, offering good performance with a low environmental impact.
Best Budget Choice: Fiberglass, adequate for dry, temperate climates but requires careful installation.
Best for Moisture-Prone Areas: Rigid foam board, especially in basement walls or exterior applications.
Ultimately, the best insulation for your project depends on your specific goals: are you prioritizing budget, energy efficiency, sustainability, or moisture control? A hybrid approach — combining two or more insulation types — may offer the best of all worlds, particularly in complex or variable climate zones.
We hope our test provides clarity for homeowners, builders, and renovators aiming to make informed decisions about wall insulation. Energy efficiency starts in the walls — and making the right insulation choice is one of the smartest investments you can make.
