The Science of the Blend: Why we blend polyester with our wool
While Thermafleece is primarily composed of British sheep’s wool (75% by weight), we incorporate a small amount of polyester to ensure the insulation remains effective for the life of the building.
Our Material Composition
- 75% British Sheep’s Wool: Providing natural insulation and moisture regulation.
- 15% Recycled Polyester Staple Fibre: Improves thermal performance and resource efficiency.
- 10% Polyester Bi-component Binder: Acts as a “glue” to hold the fibres together.
Key Benefits of the Fibre Blend
1. Permanent Structure (Thermal Bonding)
- Prevents Slumping: Insulation is subject to constant vibrations from traffic, wind, and daily activity. Without a binder, loose fibres can move and settle over time.
- Long-Term Performance: By thermally bonding the fibres in an oven during manufacture, we ensure the insulation maintains its thickness and performance for its entire service life.
- Easy Installation: The bonded structure makes the material easier to handle and install.
2. Optimising Thermal Efficiency
- Better Performance, Lower Density: Fine recycled polyester (r-PET) fibres have roughly one-third the diameter of wool. They act as “void fillers,” increasing internal surface area and reducing air movement.
- Market-Leading Results: This blend allows our UltraWool to achieve a thermal conductivity of 0.035 W/mK, making it the top-performing natural fibre insulation available.
- Cost-Effective: Because we can achieve high performance with less total material, we can offer products like CosyWool at a much more accessible price point.
3. Reduced Environmental Impact
- Lower Packaging Waste: The resilience of the blend allows for compression packing. Thermafleece requires up to 75% less packaging than non-compressed 100% wool products.
- Carbon-Efficient Transport: Compressing the insulation allows us to double the amount of product on every truck, reducing transport-related carbon emissions by up to 50%.
- UK-Made: Sourcing and manufacturing locally in the UK means our transport emissions can be 7 times lower than products shipped from central Europe.
End of Life & Circularity
Because of the polyester content, Thermafleece is not fully compostable. However, we advocate for a circular approach:
- Carbon Sequestration: Instead of composting (which releases carbon), it is better to keep the biogenic carbon locked within the wool.
- Recyclable: The insulation can be processed through standard textile recycling, where it is re-fiberised into new usable material blends.
