Skip to main content
matera.eco
Material

Sheep's Wool Insulation

How it performs, where it works, and what to check on the label

3 min readUpdated November 2026

Save guide

What is sheep's wool insulation?

Sheep's wool insulation is made from wool fibres formed into rolls, slabs, or loose fill. It is usually treated against insects and often contains a binder or recycled polyester to hold its shape. Origin varies, so ask the supplier.

How does it perform?

Declared thermal conductivity is typically around 0.035-0.040 W/mK, which is broadly similar to many mineral wool products. It takes up more depth than PIR for the same U-value, so check your build-up before specifying.

  • Sheep's wool

    0.035-0.040
    Moisture behaviour
    Hygroscopic and vapour open

  • Cellulose

    0.038-0.040
    Moisture behaviour
    Hygroscopic and vapour open

  • Wood fibre

    Often around 0.038
    Moisture behaviour
    Hygroscopic and vapour open

  • Mineral wool

    Often 0.032-0.036
    Moisture behaviour
    Vapour open, not hygroscopic in the same way

  • PIR

    Around 0.022-0.026
    Moisture behaviour
    Foil facings restrict vapour

Typical thermal conductivity. Use the declared value for the product you are buying.

Moisture: not a fix for damp

Wool insulation cannot be used to solve a damp problem. Water leaks, rising damp, and poor ventilation still need fixing, and wet insulation performs poorly.

Watch out. Hygroscopic does not mean waterproof. Keep wool dry during delivery, storage, and installation, and have moisture risk checked for solid walls and other sensitive build-ups.

What else is in it?

"100% natural" is worth checking. Wool insulation may include moth treatment, fire treatment, and polyester fibres or other binders. Polyester can be recycled and can help the product keep its shape, but it can make end-of-life recovery harder.

  • What percentage is wool, and what is the rest?
  • Is the wool from the UK or elsewhere?
  • Which insect treatment is used, and how long does it last?
  • Is an EPD available, and how does it allocate impacts from sheep farming?
  • Are offcuts or removed insulation accepted for recycling?

Fire class

Current products commonly declare Euroclass E under EN 13501-1. Some older product sheets use other test methods, so don't compare them directly. Wool insulation should be kept away from flues and heat sources, following the manufacturer's clearance instructions. Its class also limits its use in the external walls of taller buildings.

Where it works best

Wool suits timber structures where a vapour-open build-up and comfortable installation are valued. It is not rigid, so it doesn't suit every position.

  • Between joists in lofts

    Good
    Check
    Depth, ventilation, and access for services

  • Between rafters

    Good
    Check
    Ventilation, friction fit, and airtight layer

  • Timber frame walls

    Good
    Check
    Support to avoid slumping, and fire strategy

  • Suspended timber floors

    Possible
    Check
    Support from below, airflow, and pest access

  • Internal insulation on solid walls

    Needs care
    Check
    Moisture risk assessment and vapour strategy

  • External wall or flat roof insulation

    Usually unsuitable
    Check
    Consider a rigid product designed for the position

Trade-offs

Compare the installed cost and availability against other options, and follow the supplier's safety advice. Read EPDs carefully rather than assuming wool is always the lowest-carbon choice.

Using Matera

Compare thermal conductivity, thickness, wool content, treatment, and fire class across products. Ask suppliers for current Declaration of Performance documents, and compare installed cost at the thickness you actually need.

Sources

Where the facts in this guide come from. Standards and guidance change, and some sources are suppliers or trade sites, so check the original before relying on a detail.

Browse the libraryNext guideHow to Compare Insulation Materials