When it comes to building or retrofitting, insulation is often a case of “out of sight, out of mind.” However, choosing the wrong material or skimping on thickness is one of the most expensive mistakes a property owner can make.
Here is why quality and thickness matter, followed by a direct head-to-head between two entirely different insulation philosophies: Steico (wood fibre) and XPS (extruded polystyrene).
WHY QUALITY & THICKNESS MATTER
Insulation isn’t just about stopping winter cold; it is about regulating energy transfer year-round and managing moisture.
The Thickness Factor: A material’s resistance to heat flow is measured by its R-value (or thermal resistance). The formula is straightforward:
R = d / lambda
Where ‘d’ is the thickness and ‘lambda’ is the material’s thermal conductivity. Doubling the thickness doubles your thermal resistance. If you don’t use enough depth, the energy grid—and your wallet—will pay the price indefinitely.
Thermal Mass & Phase Shift: Thickness doesn’t just block cold; it delays heat. This delay is called phase shift. High-quality, dense insulation can delay the summer sun’s heat by 10 to 12 hours, keeping the interior cool until the sun goes down. Low-quality, lightweight insulation fails at this completely, regardless of R-value.
REAL-WORLD COMPARISON: STEICO VS. XPS
To understand the difference between high-quality natural insulation and standard synthetic insulation, let’s compare a Steico wood fibre board and a standard XPS (Extruded Polystyrene) board of the exact same thickness (e.g., 100mm).
FEATURE: Thermal Conductivity (lambda)
– Steico (Wood Fibre): ~0.038 W/mK (Very Good)
– XPS (Extruded Polystyrene): ~0.033 W/mK (Excellent)
FEATURE: Vapour Permeability
– Steico (Wood Fibre): Highly Breathable (mu = 3 to 5)
– XPS (Extruded Polystyrene): Vapour Barrier (mu = 80 to 250+)
FEATURE: Density & Heat Storage
– Steico (Wood Fibre): High (~150 kg/m3). Massive thermal mass.
– XPS (Extruded Polystyrene): Low (~35 kg/m3). Poor heat storage.
FEATURE: Summer Overheating
– Steico (Wood Fibre): Excellent. Long phase shift keeps heat out.
– XPS (Extruded Polystyrene): Poor. Heat penetrates quickly once saturated.
FEATURE: Acoustic Performance
– Steico (Wood Fibre): Absorbs sound efficiently.
– XPS (Extruded Polystyrene): Poor. Reflects and transmits sound waves.
FEATURE: Sustainability
– Steico (Wood Fibre): Carbon-negative, natural wood fibres.
– XPS (Extruded Polystyrene): Petrochemical-based, high embodied carbon.
VERDICT
Choose XPS only where high compressive strength and total water immersion resistance are mandatory, such as under heavy concrete floor slabs or below-ground foundation walls.
Choose Steico for walls, roofs, and timber frames. While XPS has a slightly better raw lambda value on paper, Steico wins in the real world by allowing the building envelope to breathe (preventing structural rot and mould), providing vastly superior summer heat protection, and delivering excellent acoustic dampening.
In modern building science, a high-quality, breathable envelope beats a plastic wrap every time.
Theoretical data sheets are one thing, but real-world performance over decades is what truly matters. Because we believe in building structures that last, manage moisture naturally, and offer genuine thermal comfort, Steico is the only wood fibre insulation we use on our personal projects. It is also the only system we confidently recommend to our clients. When you prioritize structural health and indoor air quality, there is simply no substitute.