Sheep wool is one of the oldest materials still used to keep buildings warm, and one of the few insulation options that regulates moisture and air quality while it does so.
It works on the same principle as it does on the animal: the crimped, tubular fibres trap pockets of still air, and still air is what slows the movement of heat. Sheep wool insulation, in batt, roll or loose-fill form, sits in the same wall, roof and underfloor cavities as glass wool or polyester, and it competes on thermal performance while behaving very differently in every other respect when it comes to humidity, indoor pollutants, fire, and cost.
This guide covers what wool insulation does well, where it falls down, what it costs in Australia, and the specific forms – batts, blown, underfloor – a specifier or owner-builder can choose between.
To read about wool composites, head over to this guide.
What wool insulation is
The product is scoured raw wool, cleaned of grease and vegetable matter, then either needle-punched into batts and rolls or processed into loose fibre for blowing. Most commercial wool insulation is not pure wool: it’s commonly blended with a proportion of recycled polyester (often around 10–15 per cent) to hold loft and structure, and it’s treated against pests and, in most markets, with a fire retardant. Those two treatments matter to the honest version of wool’s story, and they’re covered below.
Wool’s insulating ability comes from fibre architecture rather than any additive. Each fibre is covered in overlapping scales and kinked along its length, so a mass of wool holds a great many small air pockets, and the fibre walls themselves are hollow. That structure is also why the same material buffers humidity and binds certain gases – the properties are all downstream of the fibre, not bolted on.
Thermal performance: the R-value question
Insulation is compared on two related numbers. Thermal conductivity (the lambda or λ value) measures how readily a material passes heat – lower is better. R-value measures a given thickness’s resistance to heat flow – higher is better – and it’s the number that appears on Australian product labels and in the National Construction Code.
Wool performs in the same band as the mainstream materials it competes with. Peer-reviewed testing of sheep wool composites records thermal conductivity between 0.0324 and 0.0436 W/mK depending on density and thickness, which sits alongside glass wool and mineral wool rather than beating them. In practical terms, wool and glass wool of the same thickness deliver broadly comparable R-values; a recent composite study reported a maximum thermal resistance of 1.171 m²K/W for a 40 mm sample, and thicker batts scale from there. Wool does not match the state-of-the-art synthetic foams on conductivity – those achieve lower lambda values in thinner profiles – but it is squarely competitive with the fibrous insulations most Australian homes actually use.
The wool vs fibreglass comparison (or wool vs fiberglass), then, isn’t really decided on raw thermal numbers, which are close. It’s decided on everything around them.
Moisture, and why it matters
Wool’s distinguishing property is hygroscopy: it absorbs and releases water vapour without losing much thermal function. Wool can take up around a third of its own weight in moisture while still feeling dry and still insulating, buffering the humidity swings inside a building rather than letting them condense in the wall. Synthetic and glass insulations don’t do this; when moisture reaches them it tends to sit, and wet insulation both underperforms and invites mould in the surrounding structure.
This is the property that makes wool interesting in the specific conditions where fibrous insulation usually struggles – bathrooms, poorly ventilated roofs, older buildings without a modern vapour barrier. The compromise attached to it: wool manages moisture it can subsequently release, not sustained saturation. In a genuinely wet cavity – a persistent leak, ground water – no fibre insulation is the answer, and the fix is the water, not the wool.
Indoor air: the formaldehyde claim, checked
Wool is often marketed as cleaning the air, and this is the claim most worth scrutinising because it’s both real and routinely overstated. The keratin protein in wool chemically binds certain volatile organic compounds, formaldehyde chief among them – a common off-gas from engineered timber, adhesives and some furnishings. The binding is documented in peer-reviewed work: one study of sheep wool mattresses recorded a formaldehyde reduction of roughly 68 per cent over seven days, and separate testing of wool textiles reduced high formaldehyde concentrations to near zero within hours.
What the honest version withholds is any suggestion that this is permanent or unlimited. The binding capacity is finite, the rates come from chamber tests rather than lived rooms, and wool sealed inside a wall cavity is not freely exchanging air with the living space the way a carpet or an exposed panel does. The property is genuine and it’s a point in wool’s favour; it is not a reason to treat insulation as an air purifier.
Fire behaviour
Wool is difficult to ignite. Its high nitrogen and moisture content give it an ignition temperature around 560 °C, well above synthetic polymer insulations, and rather than melting or dripping it chars and self-extinguishes once the flame source is removed. It also releases comparatively little toxic smoke.
The caveat is a regulatory one and it’s important. Naturally high ignition temperature is not the same as a formal non-combustibility rating; untreated wool does not by itself meet the stringent Class A1 non-combustible classifications some applications demand, which is why most commercial wool insulation carries a fire-retardant treatment to satisfy building standards. Wool’s fire story is a real advantage over foam, stated accurately: hard to light and safer in smoke, but certified through treatment, not exempt from it.
The problems with wool insulation
There are three main downsides to using wool as an insulation.
The first is pests. Wool is a protein, and untreated it is food – the same studies that praise its performance record its low resistance to the attack of microorganisms and insects. Moths and carpet beetles will take to untreated wool. Commercial product is treated (borate and similar) to prevent this, and treated wool holds up, but the treatment is doing necessary work and its longevity is a fair question to ask a supplier.
The second is cost, covered in full below: wool is materially more expensive than glass wool for the same R-value.
The third is availability and consistency. Wool is a smaller, less industrialised supply chain than glass or polyester insulation. Fibre varies by breed and batch, fewer suppliers stock it, and lead times and product range are narrower – a constraint in Australia specifically, where the mainstream trade around wool insulation in Australia is built around bulk glass wool.
What wool insulation costs in Australia
The cost of wool insulation sits at a clear premium. As a rule of thumb it runs roughly two to three times the price of standard glass wool batts of an equivalent R-value, and the gap widens for higher R-values and for pure rather than blended product.
The premium buys the moisture and air-quality behaviour, the fire performance without petrochemical content, the low embodied carbon, and the fact that wool can be handled and installed without the skin, eye and respiratory irritation glass wool causes – no protective equipment, no itch. Whether that package justifies the cost depends entirely on the application. In a standard, well-ventilated new wall where the only job is hitting an R-value at the lowest price, it generally doesn’t. In a retrofit of an older building, a room with a moisture problem, or a project where indoor air quality and installer health are priorities, the calculation shifts.
The forms: batts, blown, underfloor
Batts. Wool insulation batts are the most common form, and the direct substitute for glass wool batts: semi-rigid panels friction-fitted between studs, joists and rafters. Sheep wool insulation batts are the default for new-build walls and accessible roof spaces, and where most of the material is specified.
Blown and loose-fill. Blowing wool insulation as loose fibre reaches cavities and roof spaces that batts can’t easily fill – irregular gaps, existing closed walls, awkward roof geometry. Blown wool suits retrofit particularly, where opening a wall to fit batts isn’t practical.
Underfloor. Wool underfloor insulation is fitted as batts or rolls between floor joists beneath a suspended floor. Wool’s moisture behaviour is a genuine advantage underfloor, where subfloor humidity is often higher and where a material that can take up and release moisture without holding it is better matched to the conditions than one that traps it.
Sound insulation. Wool sound insulation is also specified for acoustic rather than thermal reasons. Its fibre structure absorbs airborne sound well, and testing has found wool panels’ sound absorption comparable to mineral wool, and at some frequencies better – useful in internal walls and between-floor assemblies where the goal is quiet rather than warmth.
Embodied carbon
Wool’s production carbon is low relative to the synthetic and mineral alternatives. Embodied carbon – the emissions from producing and transporting a material, before it does any work in the building – is where wool’s renewable origin tells. One life cycle assessment cited in recent bio-composite research put sheep wool at roughly 5.4 kg CO₂-equivalent per cubic metre against approximately 135 kg for a comparable volume of mineral wool. This is a large gap, and it’s the strongest environmental argument for the material. The usual caveat applies: LCA figures depend heavily on system boundaries, transport distance and whether the wool is a recycled or waste stream, so a single ratio is indicative rather than a specification.
Where wool insulation is the right answer
Not everywhere, which is the point. In a straightforward new build chasing an R-value at the lowest cost, glass wool remains the rational default and wool’s premium is hard to justify. Wool earns its place in the conditions the mainstream materials handle worst: retrofits of older, moisture-active buildings; roofs and subfloors where humidity swings; rooms where indoor air quality matters; and projects where the embodied carbon of the insulation, and the health of the person installing it, are part of the brief rather than an afterthought. It’s a considered choice for specific conditions, not a like-for-like swap dressed up as a virtue.
Explore local wool-based products on the directory, including Wisewool.
1. Analysis of Sheep Wool-Based Composites for Building Insulation (2022) | Polymers
2. Valorisation of Sheep Wool Fibres in Sustainable Energy-Efficient Materials: Thermal and Acoustic Properties of Bio-Based Composites for Low-Carbon Construction (2026) | Energies
3. Improving Indoor Air Quality by Using Sheep Wool Thermal Insulation (2021) | Materials
4. Improving indoor air quality and mitigating health risks with sheep wool as a sustainable material (2025)
5. Sheep’s wool insulation: A sustainable alternative use for a renewable resource? (2014) | Resources, Conservation and Recycling
6. Exploring the potential of sheep wool as an eco-friendly insulation material: A comprehensive review and analytical ranking (2023) | Case Studies in Construction Materials
