Ashden Winners

Second Nature / Insulating buildings using sheep’s wool

Area of work:

Second Nature’s Ashden Award recognised the work it had done to commercialise a product made from under-utilised sheep’s wool, for insulating buildings.

Significant amounts of coarse wool produced in the UK go to waste, because it is not suitable for modern textiles. However, it could be used for insulating buildings, particularly historic buildings where wood might rot if conventional insulation materials were used. Second Nature developed and brought to market Thermafleece, a roof-insulation material made from sheep’s wool.

By 2010, over 200,000 m2 of Thermafleece had been sold.

The estimated carbon dioxide saving from insulating a typical loft with 200 mm of Thermafleece is about 1.2 tonnes/year.

In 2005, Second Nature used 20,000 kg of coarse wool a month, much of it from the local area.

"The historic flocks of Herdwick sheep have been linked with this terrain for generations. The use of their wool in Thermafleece is helping to ensure the continuing viability of this particular element of the UK’s farming heritage."

Chris Baines, writer and broadcaster

Key points

  • Web of 85% wool fibres and 15% polyester fibres is passed through a bonding oven, where polyester bonds wool together, providing a compressible insulating material with structure and stability.
  • Thermafleece then made moth and insect proof through a patented process using Roxin, a naturally occurring mineral.
  • By 2004, over 100,000 m2 of 100 mm thick Thermafleece had been sold, enough to insulate about 1,100 lofts. Customers include those with historic houses, where breathability and moisture permeability is essential.
  • Annual saving of about 1,300 tonnes/year CO2.
  • Product has a low-input manufacturing process, thus a much lower embodied energy than alternatives – estimated at 14% of that in glass fibre insulation.
  • Thermafleece is safe to handle, and converts a waste (coarse wool) into a resource.
  • It provides a market for local coarse wool, leading to extra income for hill farmers and hence the protection of rural jobs and landscapes.


The idea for Thermafleece developed when Christine Armstrong renovated a 17th Century farmhouse and found that the only sheep’s wool insulation available in the UK was imported. Christine researched the UK woollen industry and found that the coloured, coarse wools from hill-farmed sheep only had limited use in the modern textile industry and so often went to waste. Turning this wool into insulation converted it from a waste into a resource.

The organisation

Second Nature UK was incorporated as a limited company in 2000 and the product Thermafleece was launched in 2001. The company is owned by its Directors Christine Armstrong and David Baldry.  In 2009, nine people worked for Thermafleece and two for Edenbloc. Sales are national.

The technology

How is it made?

Thermafleece is essentially a web of wool fibres, bonded by polyester into light, compressible slabs between 50 and 100 mm thick. It is insect- and fire-proof and can last the lifetime of a building.

Manufacture takes place in Yorkshire, and makes use of the facilities of the existing local woollen industry for some of the processing.

Thermafleece achieved British Board of Agrément accreditation in September 2002, which means that it fully complies with building regulations for roof and timber frame wall applications. This is very important in the construction industry.

The product also has accreditation from the Energy Savings Trust as an energy savings measure that can be used in government-supported programmes, such as energy efficiency activities funded through CERT.

Laying thermafleece in a loft: the material is safer to handle than mineral wool.

The technology in more detail

Second Nature UK worked for two years in conjunction with the University of Leeds and other specialists to develop the Thermafleece manufacturing process.  Once the coarse wool has been collected, it is scoured (washed), and put through a purpose-designed ‘air laying’ machine which forms a homogeneous web of wool fibres at the required height. Next, the web of wool (which forms 85% of the material) and polyester fibres (which form the remaining 15%) are passed through a bonding oven, where the polyester fibres bond the wool together, providing the insulation with the necessary structure and stability. The Thermafleece is then made moth and insect proof through a patented process using a naturally occurring mineral called Roxin. This kills insects through electrostatic rather than chemical action.


Environmental benefits

Thermafleece reduces heat loss from buildings and thus heat demand and carbon emissions, and improves thermal comfort. Its thermal insulation properties are very similar to those of conventional mineral insulation and it can be used in both retrofit and new build projects.

The estimated carbon dioxide saving from insulating a typical loft with 200 mm of Thermafleece is about 1.2 tonnes/year. Based on sales up until 2004, total savings were estimated at 1,300 tonnes/year CO2.

Because Thermafleece is largely made from sheep’s wool and with a low-input manufacturing process, it has a much lower embodied energy than conventional alternatives – estimated at only 14% of that in glass fibre insulation.

Thermafleece has been used in National Trust properties and historic buildings because of its moisture permeability; conventional insulating materials might cause moisture accumulation and cause wood to rot.

Economic and employment benefits

Production of Thermafleece creates a market for coarse wool, providing an additional source of income for hill farmers and thus the protection of rural jobs and landscapes. In 2005, Second Nature used 20,000 kg of coarse wool a month, much of it from the local area.  Herdwick sheep in particular are a historic indigenous breed and this, and other, historic breeds are directly supported by the production of Thermafleece.

Other benefits

Because it costs more than conventional insulation materials, Thermafleece has been used in historic buildings where conventional materials were unsuitable. It has also been used in projects promoting best sustainable practice such as schools and social housing projects.

Thermafleece can be handled without specific protection requirements, and is therefore very valuable for DIY installations and in buildings used by people who might be particularly sensitive to air contamination. Thermafleece can also help create breathable constructions, because it regulates the humidity balance through absorption and desorption of water from the wool fibres.  It is easy to recycle and largely biodegrades at the end of its useful life.

Update: what happened next?

By the end of 2009, about 200,000 m2 of Thermafleece had been sold, saving an estimated 2,400 tonnes/year of CO2. Two additional types of Thermafleece were on the market. One uses less wool and additional polyester, so that it is compressible and suitable for filling awkward spaces.  The other uses fibres from UK-grown hemp and recycled polyester.

The Ashden Awards prize money was used to support the testing of ‘Edenblock’ a new type of low-density rigid insulation board, suitable for insulating the inside of solid walls and lofts, Edenbloc is largely made from recycled wool, and is moisture-permeable and breathable like Thermafleece. This product was launched in March 2010.

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