Sheep's Wool Insulation

Material Type

Animal-Fiber Thermal Insulation

Material Description

Sheep's wool insulation is exactly what it sounds like — wool fibers, cleaned, lightly carded, and batted into mats or loose-fill. The keratin protein in wool is naturally hygroscopic: it can absorb and release up to 35% of its weight in moisture without losing R-value, which makes it remarkable at buffering humidity swings inside a wall cavity. Wool is also naturally flame-resistant — it self-extinguishes rather than burning, because keratin has a high nitrogen content and a high autoignition temperature. Manufacturers typically treat wool with borate for insect resistance; borate is itself low-toxicity to mammals and the levels used pose negligible health risk. End-of-life: compostable.

Composition & Origin

Sheep's wool fiber — keratin protein backbone, naturally crimped, hygroscopic, with a thermal conductivity ≈ 0.038 W/m·K

Health Profile — All Endpoints Clear

Severity scored 0–10 against the same 10 hazard endpoints we use for the chemical families on the avoid list. Every score is 1–2 — essentially no signal across every endpoint.

Common Forms & Brands

• Havelock Wool batts and loose-fill
• Black Mountain Insulation NatuWool
• Oregon Shepherd loose-fill wool
• Common framing: 100% wool batts, wool/borate batts, dense-pack loose-fill

Why We Use It

• No off-gassing — wool is the cured product, not a reactive chemistry
• Naturally flame-resistant — self-extinguishes, no added flame retardants required
• Moisture-buffering — absorbs and releases water vapor without losing R-value
• Biodegradable at end of life — compostable rather than landfill-bound
• Carbon-storing — sequesters atmospheric carbon in the keratin protein

Where It Performs Best

• Wall cavity insulation (batts) in stud and rafter bays
• Loose-fill attic insulation (dense-pack capable)
• Acoustic insulation in interior partitions
• Sound-deadening between floors

Building Applications for Sheep's Wool Insulation

Listed alphabetically. Where in a home this material earns its keep.

• Attic Loose-Fill
• Cathedral Ceiling Cavity
• Floor Joist Bays
• Interior Sound Partitions
• Rim Joist Air Seal Backing
• Wall Cavity Batts