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Material profile  ·  Bio-based  ·  Construction & Interior Design

Sheep Wool Insulation: Properties, Fire, Carbon and Standards

What sheep wool insulation is, what its datasheets, EPDs and approvals actually say about conductivity, fire, moth treatment and carbon, and where the evidence stops.

ArchitectsInterior designers

By Pilar Flores· Published October 7, 2026· Updated October 8, 2026· 9 min read

Sheep wool insulation properties at a glance

Family
Bio-based, animal-fibre thermal and acoustic insulation (sheep wool, often with a polyester binder)
Origin
Shorn sheep wool, collected regionally and washed before processing. Thermafleece states British wool;[6] the Isolena EPD describes regional collection centres and washing with water and soda, and says the wool comes from Europe, mostly Austria, Spain, Germany, the Netherlands and France.[5]
Production
Washed wool is opened and carded into a fleece. Thermafleece thermally bonds it with a PET bi-component binder;[6] Isolena consolidates it mechanically by needling, with no adhesive or support fibre, per its EPD.[5] Loose-fill wool is washed and whitened and has no binder.[3]
Forms
Rolls and slabs (Thermafleece CosyWool roll, 25–150 mm)[1] · needled rolls from 3.5 to 300 mm (Isolena)[5] · loose fill for roof cavities and ceilings (NITA-WOOL)[3]
Thermal conductivity (λ)
0.039 W/(m·K) for Thermafleece CosyWool roll at 18 kg/m³;[1] 0.037 average for the Isolena range, with 0.033 stated for its 30 kg/m³ Klemmfilz;[5][2] 0.0493 for loose-fill NITA-WOOL at 18 kg/m³, per its ETA.[3] All are manufacturer-declared values.
Density
18 kg/m³ (CosyWool roll) to 31 kg/m³ (UltraWool slab);[6] 18 to 100 kg/m³ across the Isolena range, 23.26 kg/m³ on average.[5]
Reaction to fire
Euroclass E for Thermafleece CosyWool (declared by the manufacturer under system 4, no notified body);[4] D-s2,d0 on the two Isolena datasheets we read, while its EPD gives B, C or D classes depending on the product;[5][2] B-s3,d0 for borate-treated NITA-WOOL.[3]
Embodied carbon (A1–A3)
Thermafleece CosyWool roll, per m² at R = 1 m²K/W: 0.90 kg CO₂e fossil, −0.86 biogenic, 0.05 total.[6] Isolena, per m³ at 23.26 kg/m³: 16.9 kg CO₂e fossil, −36.4 biogenic, −19.3 total.[5] Different declared units, so the two are not comparable.
Emissions
Thermafleece reports formaldehyde below 2 µg/m³ at 3 and 28 days and TVOC of 9 µg/m³ at 3 days (not detected at 28), from its declaration of performance.[4] natureplus certificate 0103-099-0101 covers the Isolena range, valid to 12/2029.[7]
Moisture behaviour
Hygroscopic. Thermafleece lists 7.21 % moisture content by mass at 50 % RH and 14.84 % at 95 % RH on sorption;[1] the NITA-WOOL ETA sets a critical moisture content of 75 % and a vapour resistance factor µ of 1 to 4.[3]
Certifications seen
International EPD System S-P-04468 (Thermafleece)[6] · Bau EPD, natureplus and ETA-07/0214 (Isolena)[5][7][2] · ETA 10/0330 (NITA-WOOL).[3] See the supplier table.

Sheep wool insulation suits designers who want a fibre insulation that is not mineral, not foam and not wood. It is also a product where details matter: the binder, the moth treatment and the fire class all change from one maker to the next.

This guide sets out what the sources we read support. Most numbers come from manufacturers, so we say so where it applies.

What is sheep wool insulation, and how is it made?

Mats, rolls and loose fill

Sheep wool insulation comes as factory-made mats and rolls or as loose-fill fibre. Mats are carded wool consolidated either by needling or by a thermally bonded binder. Thermafleece CosyWool, for example, is 75 % wool by mass, with about 15 % recycled PET and 10 % PET binder in the EPD's content table (0.527 kg wool in 0.702 kg of product per m² at R = 1).[6] Isolena says its mats are 100 % pure sheep's wool without synthetic additives or supporting fibres.[2] NITA-WOOL is loose, washed and whitened wool without binder, installed by hand.[3]

Which standard applies?

Mineral wool insulation is covered by the harmonised standard EN 13162, whose BSI catalogue entry describes factory-made mineral wool products.[8] Sheep wool is not in that standard. Thermafleece's declaration of performance lists no harmonised technical specification and no notified body, and the manufacturer declares under system 4.[4] Isolena and NITA-WOOL instead rely on European Technical Assessments (ETA-07/0214 and ETA 10/0330) issued under European Assessment Documents, EAD 040005-00-1201 for factory-made products of vegetable or animal fibres and EAD 040456-00-1201 for in-situ loose fill of animal fibres.[2][3] There is also ISO 17749:2018, which covers factory-made mats and boards with more than 50 % natural sheep wool by mass, the balance being polymeric material.[9] We did not find which of these a given project's building authority will accept, so check that before you specify.

How well does sheep wool insulate?

Declared conductivity

Declared λ values sit in a narrow band for mats: 0.039 W/(m·K) for CosyWool roll at 18 kg/m³ and 0.037 on average for Isolena, with 0.033 stated for its 30 kg/m³ felt.[1][5][2] Loose fill is higher. NITA-WOOL's ETA gives 0.0493 at 18 kg/m³ and tells designers to calculate with installed thickness minus 10 % for settlement.[3] An academic study by Zach and colleagues, from the Brno and Vienna technical universities, tested sheep wool insulation under several conditions and reports performance comparable to mineral wool; we read the abstract only.[10]

Moisture and humidity

Wool takes up water vapour from the air. Thermafleece publishes a sorption curve from 4.56 % moisture by mass at 30 % relative humidity to 14.84 % at 95 %, and the desorption curve sits above it.[1] The Isolena EPD states that wool absorbs up to 33 % of its weight, which is a company claim.[5] The limits are in the ETAs. NITA-WOOL must not be exposed to precipitation or wetting, and its critical moisture content is 75 %.[3] In a laboratory study, four 30–35 kg/m³ wool mattresses had sorption curves below their desorption curves, meaning they held on to some water as humidity fell.[11]

Is sheep wool insulation fire safe?

Not by default, and not uniformly. Thermafleece CosyWool is declared Euroclass E, with a flammability and smoulder test to BS 5803-4 and a small-flame test to EN ISO 11925-2.[4] Isolena's EPD lists B-s1,d0, C-s2,d0 or D-s2,d0 depending on the product. Its datasheets for the 18 and 30 kg/m³ felts both give D-s2,d0, and the 18 kg/m³ sheet gives B-s1,d0 only for a tested system, a perforated acoustic ceiling panel lined with 40 mm of wool.[5][2] Loose-fill NITA-WOOL reaches B-s3,d0 with disodium octaborate tetrahydrate as the flame retardant.[3] Check the class of the exact product and thickness, and the national rule for the building type. We did not read any large-scale or façade fire test on wool insulation.

What treatments are used against moths, and are they safe?

Wool is keratin, and the documents we read treat keratin-digesting insects, moths and beetles among them, as the risk, so every product needs some protection.[3][5] The documents we read show three approaches. NITA-WOOL's ETA names permethrin as the anti-insect treatment and requires the insulation to be covered to avoid direct contact with building users.[3] Isolena describes a plasma-ion treatment, Ionic Protect, that it calls biocide-free and says leaves the fibre inedible to keratin-digesting insects; this is the maker's claim.[5] Thermafleece reports a pass to ISO 3998 for clothes moth resistance;[4] its datasheet, declaration of performance and EPD name no treatment, but its website says all its wool is treated with sodium borate (borax) fire retardant and is protected from clothes moths without added biocides, which is the maker's claim.[15] An older ETA for another product notes a long-term test in which no new generation of insects hatched, which is the type of evidence to ask for.[12] The Isolena datasheet also lists no borates toxic to reproduction under EN 16516.[2]

Does sheep wool improve indoor air?

Two separate things get blended in marketing. First, emissions from the product. Thermafleece reports formaldehyde below 2 µg/m³ and TVOC of 9 µg/m³ at 3 days in chamber testing (TVOC to EN 16516, formaldehyde to ISO 16000-3), from its own declaration.[4] Isolena holds natureplus certificate 0103-099-0101, which lists climate protection, healthy living and resource conservation in its scope.[7]

Second, the claim that wool removes pollutants from room air. The peer-reviewed work we read supports a narrower statement. Mansour and co-authors (Bangor University, 2016) report that wool absorbs formaldehyde, toluene, limonene and dodecane, in amounts that depend on the sheep breed and the processing.[13] Hegyi and co-authors (2021) measured a 44 mm wool mattress in a 119-litre chamber at about 100 µg/m³ formaldehyde: 68–69 % was consumed over seven days, and only 13 % came back out within 24 hours.[11] These are small-chamber results on insulation samples. We found no field study showing a measurable effect on air in an occupied building, and a sheep wool layer behind an airtight, covered build-up has little contact with room air.

How much carbon is in sheep wool insulation?

What the EPDs show

Both EPDs we read are third-party verified. Thermafleece's, registered with the International EPD System as S-P-04468, was verified by Dr Hudai Kara, valid to 31 October 2026 (the International EPD System registry listed it as valid on 8 October 2026, so it expires within weeks; a registry search for Thermafleece that day found no renewed or replacement EPD), and uses economic allocation between wool and meat.[6] Per m² of CosyWool roll at R = 1, A1–A3 fossil GWP is 0.90 kg CO₂e, biogenic GWP is −0.86 and the total is 0.05.[6] Isolena's Bau EPD, for the 2023 output of its Waizenkirchen plant, gives A1–A3 fossil GWP of 16.9 kg CO₂e per m³ at 23.26 kg/m³, biogenic −36.4 and total −19.3.[5] The English PDF hosted by the licensee prints both its issue and validity dates as 2025-12-05. The Bau EPD programme's own register lists the declaration as issued 12.05.2025 and valid to 12.05.2030, with the same GWP figures in its PDF; ÖKOBAUDAT and baubook give the same dates (all checked 8 October 2026). The register also lists an earlier declaration, BAU-EPD-Isolena-2024-1, issued 23.10.2024 and valid to 23.10.2029.[5]

Why a negative number needs care

The biogenic credit is the carbon stored in the wool. Thermafleece's EPD puts +0.895 kg CO₂e back in module C4 for the roll, and Isolena's puts +36.4 in C3 on incineration.[6][5] Thermafleece's own datasheet shows 0.95 kg CO₂e for A1–C4 per functional unit.[1] The declared units differ (per m² at fixed R-value against per m³), and the CosyWool figures include PET. A doctoral thesis by Andrew Norton (Bangor, 2008) compared hemp and sheep wool insulation with mineral wool and found particularly low or absent global warming potential for the natural fibres because of sequestered carbon; we read the abstract only. The Thermafleece EPD names a Dr Andrew Norton (Renuables Ltd) as its LCA author; we did not confirm he is the thesis author.[14][6] We found no like-for-like EPD comparison with wood fibre or mineral wool, and make none. See wood fibre insulation and hemp for the neighbouring bio-based options.

Where is sheep wool insulation used?

Timber-frame walls, roofs and floors

Best for: architects · self-builders

Thermafleece lists thermal and acoustic insulation for walls, floors and roofs,[4] and Isolena lists roofs, walls, façades, ceilings and floors.[5] The NITA-WOOL ETA sets limits for that loose-fill product: no compression loads, and it must stay dry.[3] We did not read installation guidance for the mats.

Loft and ceiling loose fill

Best for: retrofit · architects

NITA-WOOL's ETA covers closed cavities in horizontal or pitched (≤ 10°) roofs and accessible top-storey ceilings without foot traffic.[3] Settlement is stated: up to 9.5 % under impact at 18 kg/m³ and 330 mm.[3]

Acoustic lining and product design

Best for: interior designers · product designers

Thermafleece reports a weighted sound absorption of 1.00 at 100 mm,[4] and Isolena lists acoustic ceilings and partitions.[2] We found no sourced guidance on wool insulation in furniture or product design.

Which suppliers make sheep wool insulation?

Suppliers selected by our editors from documents we read. We list three whose datasheets, EPDs or ETAs we could open.

SupplierProductsCountryCertifications
Eden Renewable Innovations (Thermafleece) CosyWool roll and slab, UltraWool slab; wool with recycled and bi-component PET United Kingdom EPD S-P-04468, International EPD System, verified, valid to 31 Oct 2026 (registry status "Valid" seen 8 Oct 2026, no renewal listed).[6] Declaration of performance: Euroclass E, system 4.[4] The maker's certificates page (8 Oct 2026) lists ISO 9001, ISO 14001 and the EPD; no BBA certificate or declaration of performance appears there.
Isolena Naturfaservliese Needled wool mats (Optimal, Klemmfilz, Block and others), loose wool Austria ETA-07/0214 (listed in the EOTA database, issued by OIB, version 1, 16 Nov 2017) and natureplus 0103-099-0101 (valid to 12/2029, listed as certified in the natureplus product database on baubook, 8 Oct 2026);[2][7] Bau EPD declaration BAU-EPD-Isolena-2025-1, issued 12 May 2025, valid to 12 May 2030 (Bau EPD register, 8 Oct 2026).[5]
RMT Insulation (NITA-WOOL) Loose-fill wool with borate and permethrin treatment Spain ETA 10/0330 issued by ITeC on 22 March 2017: B-s3,d0, λD 0.0493.[3] The EOTA database lists it as version 1 with no later version; we found no expiry or withdrawal date.[3]

Certificates are summarised from the documents named in the sources. On 8 October 2026 we also checked the International EPD System registry (Thermafleece), the Bau EPD register, ÖKOBAUDAT and the natureplus product database as hosted on baubook (Isolena), and the EOTA database (both ETAs, no later versions listed). natureplus's own certificate page showed no details for 0103-099-0101 and points to that database. Confirm current status with the issuing body before specifying. Listing policy: editorial selection, not paid.

Frequently asked questions about sheep wool insulation

What is the thermal conductivity of sheep wool insulation?

Manufacturers declare 0.033 to 0.039 W/(m·K) for mats and 0.0493 W/(m·K) for one loose-fill product. These are declared values, not independent measurements.

Is sheep wool insulation fire resistant?

It depends on the product. Declared classes in the documents we read run from Euroclass E to D-s2,d0 for mats and B-s3,d0 for one borate-treated loose fill, plus one tested ceiling system at B-s1,d0. Check the class of the exact product.

How is sheep wool insulation protected from moths?

By treatment. One ETA names permethrin, one maker describes a biocide-free plasma-ion process, and one says it uses borax and reports an ISO 3998 pass.

Does sheep wool insulation absorb moisture?

Yes. Thermafleece lists 7.21 % moisture by mass at 50 % relative humidity and 14.84 % at 95 %. Loose fill must be kept dry, and one ETA sets a critical moisture content of 75 %.

Does sheep wool insulation remove formaldehyde from air?

In chamber tests on samples, yes: one study measured 68–69 % consumption over seven days. We found no study showing an effect in occupied buildings.

What is the carbon footprint of sheep wool insulation?

Two EPDs show near-zero or negative A1–A3 totals because stored biogenic carbon is credited, then released at end of life. The fossil part is 0.90 kg CO₂e per m² at R = 1 for one product.

Which standard covers sheep wool insulation?

Not EN 13162, which covers mineral wool. Products use ETAs, and ISO 17749:2018 sets a specification for mats and boards with more than 50 % sheep wool.

The bottom line on sheep wool insulation

Sheep wool insulation is a credible fibre insulation with declared thermal values close to other mat insulations, and verified EPDs exist for two makers. The decisions sit in the details: the binder content, the fire class of the exact product, the moth treatment and whether the build-up keeps the wool dry. Ask each supplier for its ETA or declaration of performance, the treatment chemistry and the EPD.

Related materials

Wood fibre insulationBio-based Hemp & hempcreteBio-based CorkBio-based Straw baleBio-based

Sources

  1. Eden Renewable Innovations Ltd (undated). Thermafleece CosyWool Roll Technical Data Sheet, version 7, read on the maker's site on 8 October 2026. Source for λ, density, thicknesses, vapour sorption values, µ and the A1–C4 GWP line. Manufacturer document (company claims). Full text read. The earlier version 4 (18 Jan 2024; distributor copy, PDF) carries the same λ, density, sorption and GWP values and lists thicknesses from 50 mm. PDF (maker's site)
  2. Isolena Naturfaservliese GmbH (2025–2026). Technical data sheets Klemmfilz 30 kg/m³ (version 29.01.2025) and Optimal 18 kg/m³ (version 26.01.2026). Source for λ, fire class, ETA-07/0214 reference, borate statement and product forms. Manufacturer documents (company claims). Full text read. Optimal PDF · Klemmfilz PDF. We did not open ETA-07/0214 itself; its EOTA database record was read: EOTA record.
  3. ITeC (2017). European Technical Assessment ETA 10/0330, NITA-WOOL, RMT Insulation, issued 22.03.2017 under EAD 040456-00-1201. Source for composition and treatments, fire class, λ, moisture limits, settlement and intended use. Independent technical assessment body (EOTA member), manufacturer-commissioned. Full text read; the EOTA database record (EOTA record) lists version 1 only and gives its issue date as 21/03/2017, one day before the document's 22.03.2017. PDF
  4. Eden Renewable Innovations Ltd (2019, signed 2022). Declaration of Performance: Thermafleece CosyWool. Source for the declared λ range, Euroclass E, ISO 3998 moth test, emissions test results, system 4 and the absence of a harmonised specification or notified body. Manufacturer document (company claims). Full text read. The maker's certificates page lists no declaration of performance, so this is a distributor's copy. PDF (copy hosted by a distributor)
  5. Isolena Naturfaservliese GmbH (2025). EPD: ISOLENA sheep's wool insulation, Bau EPD GmbH, BAU-EPD-Isolena-2025-1-Ecoinvent-Schafwolldämmung, issue date printed as 2025-12-05; LCA by IBO GmbH; two named verifiers. Source for production, A1–A3 figures, density, fire class range and treatment description. Programme-verified; the product description includes company claims. The licensee's English PDF prints issue and validity dates as 2025-12-05. The Bau EPD register (entry, German PDF read: GWP figures identical) shows issue 12.05.2025 and valid to 12.05.2030; ÖKOBAUDAT (dataset) lists 2025-05-12 and valid to 2030, and baubook (listing) lists 12 May 2030 (all read 8 October 2026). Full text read. PDF
  6. Eden Renewable Innovations Ltd (2021). Environmental Product Declaration: Thermafleece CosyWool, UltraWool, International EPD System, registration S-P-04468, published 2021-11-01, valid to 2026-10-31; LCA by Dr Andrew Norton (Renuables Ltd); third-party verifier Dr Hudai Kara (Metsims). Source for composition, A1–A3 and biogenic carbon figures, allocation, and the formaldehyde test note. Manufacturer-owned, independently verified. Full text read; the registry page showed status Valid, validity date 2026-10-31, on 8 October 2026, and a library search for Thermafleece returned no other EPD for these products. environdec.com/library/epd4468
  7. natureplus e.V. (2025). Certificate 0103-099-0101, insulating material made of sheep wool, licensee Isolena Naturfaservliese GmbH, issued 2025-04-14, valid to 12/2029. Independent certifier; the certificate PDF was read. natureplus's own certificate page shows no details and points to its product database, which is hosted on baubook; that listing (listing) shows the certificate number 0103-099-0101 as certified, valid until 31 December 2029 (read 8 October 2026). PDF (hosted by the licensee)
  8. EN 13162, Thermal insulation products for buildings – Factory made mineral wool (MW) products – Specification. Title and scope taken from the BSI catalogue entry for BS EN 13162:2012+A1:2015; the standard text was not read; harmonised status confirmed in a Czech standards listing (nlfnorm.cz). Independent standards body. BSI shop listing
  9. ISO 17749:2018, Thermal insulation products – Sheep wool mat and board – Specification, as adopted by BSI (BS ISO 17749:2018, published 31 May 2018). Scope (factory-made mats and boards, more than 50 % natural sheep wool by mass, balance polymeric) taken from the BSI catalogue page; the standard text itself was not read. Independent standards body. BSI catalogue page
  10. Zach, J., Korjenic, A., Petránek, V., Hroudová, J. & Bednar, T. (2012). "Performance evaluation and research of alternative thermal insulations based on sheep wool." Energy and Buildings 49:246–253. Peer-reviewed; only the abstract on the Brno University of Technology publication page was read. Independent. VUT record
  11. Hegyi, A., Bulacu, C., Szilagyi, H., Lăzărescu, A.-V., Meiţă, V., Vizureanu, P. & Sandu, M. (2021). "Improving Indoor Air Quality by Using Sheep Wool Thermal Insulation." Materials 14(9):2443. Peer-reviewed, open access; the PMC full text (PMC8125880, via Europe PMC) was read directly and the bibliographic data checked against Crossref. Independent. doi:10.3390/ma14092443
  12. Deutsches Institut für Bautechnik (2013). European Technical Approval ETA-03/0035, Alchimea lana Dämmvlies, valid 13 June 2013 to 13 June 2018 (expired; used only as an example of the test evidence). Independent approval body. Full text read. PDF
  13. Mansour, E., Curling, S., Stéphan, A. & Ormondroyd, G. (2016). "Absorption of volatile organic compounds by different wool types." Green Materials 4(1). Peer-reviewed; abstract read via Crossref. Independent. doi:10.1680/jgrma.15.00031
  14. Norton, A. (2008). The life cycle assessment and moisture sorption characteristics of natural fibre thermal insulation materials. PhD thesis, Bangor University. Abstract read on the university research portal; the full thesis was not read. Independent academic work; the thesis author shares a name with the Thermafleece LCA author, and the Renuables website lists Dr Andrew Norton as director alongside Prof Callum Hill, the thesis supervisor named on the Bangor record, but no document we read states they are the same person. Bangor research portal
  15. Eden Renewable Innovations Ltd (June 2026). Insects and Durability, news and technical information page on thermafleece.com, and the Safety & Technical FAQ ("How does Thermafleece react to fire?"). Source for the borax (sodium borate) treatment and the statement that no added biocide is needed. Manufacturer web pages (company claims); read in full on 8 October 2026. thermafleece.com
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