Investigating the Properties of Sheep's Wool Fleece as a Thermal Insulating Material

Categories: Physics



The purpose of this report is to investigate the properties of sheep’s wool fleece used as a thermal insulating material. This report examines its suitability for use as a thermal insulator in various applications, particularly in structures like rafters.


The main objectives of this report are to analyze the different properties of sheep's wool fleece and determine whether it is suitable for thermal insulation.


Physical Properties

Physical properties play a crucial role in determining the suitability of a material for a specific application, such as thermal insulation.

These properties include size, density, and shape.


Sheep’s wool insulation comes in varying thicknesses, with the most common options being 50mm, 75mm, 100mm, and 150mm. It is also designed in widths of 370mm and 570mm (Just Insulation, 1998).


Sheep wool insulation has a density of 31 kg/m3 (thermafleece, 2000). In comparison to other insulation materials, sheep wool exhibits lower density, as shown in the table below:

Comparison of Densities of Different Insulating Materials
Material Density (kg/m3)
Sheep Wool Insulation 31
Mineral Wool 40
Fiberglass 35
Cellulose 50


Materials used for thermal insulation come in various shapes, including batts, boards, rolls, spray foam, loose fill, and aggregate.

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Sheep's wool insulation is available in batts and rolls, making it easy to handle and install (Hunt, 2020).

Mechanical Properties

Mechanical properties are essential for assessing the durability and potential of a material. Key mechanical properties for sheep's wool insulation include stress, strain, elasticity, thermal conductivity, R-value, thermal diffusivity, specific heat capacity, and vapor permeability.

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Stress and Strain

Sheep wool exhibits peak elongation at break, with a range of 25% to 35%. It has a tensile strength ranging from 120 MPa to 174 MPa and a Young's Modulus between 2.3 GPa to 3.4 GPa. Different strain rates (260, 340, 370, and 610/s) yield varying tensile stress-strain curves (Parlato & Porto, 2020).


Sheep wool insulation demonstrates high elasticity, ensuring that it does not settle over time, maintaining its performance (ecomerchant, 1999).

Thermal Conductivity

Sheep wool insulation has a thermal conductivity ranging from 0.035 to 0.04 W/mK, making it an effective insulating material. Compared to mineral wool, which has a thermal conductivity of 0.044 W/mK, sheep wool exhibits a lower λ-value, indicating superior insulating properties (thegreenage, 2017).

Thermal Resistance

Sheep wool possesses an R-value ranging between 3.5 to 3.8 per inch, surpassing R-values of substitutes like cellulose, fiberglass, and mineral wool. Its higher R-value is attributed to its crimped nature, which traps air in minute bubbles (Roberts, 2019).

Thermal Diffusivity

Thermal diffusivity is a material-specific property that measures the ability of a material to conduct thermal energy relative to its capacity to retain thermal energy. The thermal diffusivity of sheep's wool is 1.03 m2/s (Parlato & Porto, 2020).

Specific Heat Capacity (Thermal Capacity)

The specific heat capacity of a material indicates the amount of heat required to raise the temperature of 1 kg of the material by 1℃ or 1K. Higher thermal capacity means the material absorbs more heat before its temperature rises significantly, making it a better insulator. Sheep wool has a specific heat capacity of 1800 J/kgK (greenspec, 2002).

Vapor Permeability

Sheep's wool fiber is hygroscopic, meaning it absorbs water vapor. Additionally, it can absorb and release water (hydrophilic). This property makes it suitable for use in loft spaces, where it can absorb up to 33% of its mass in moisture without compromising its insulating properties (Burton Roofing Merchants Ltd, 2019).

Chemical Properties

Chemical Composition

The chemical composition of sheep wool insulation is detailed in the table below:

Chemical Composition of Sheep's Wool Insulation
Component Percentage (%)
Protein 45%
Water 25%
Lipids 15%
Minerals 10%
Other 5%

Chemical Treatment

Sheep wool undergoes thorough cleaning and treatment with borax to make it resistant to insects and enhance its non-flammable properties. Borax is dissolved in boiling water and sprayed onto the wool. This treatment not only provides insect resistance but also ensures the material remains robust even when exposed to moisture (thegreenage, 2014).

Optical Property


The color of sheep wool insulation varies from grey/black to white, with the possibility of dyeing it in various colors except for black, which is restricted to dark shades (Sheep Wool Insulation, 2004).

Acoustical Property

Sound Absorption

An experimental model proposed by Delany-Bazley was used to evaluate the sound absorption properties of different sheep wool samples. The results indicated that sheep wool insulation performs well in sound absorption, particularly at medium frequencies, surpassing the performance of wool or polyurethane insulation materials (Rey, et al., 2017).

Physiochemical Property

Physiochemical properties pertain to the changes observed in a material due to moisture and other environmental factors. Sheep's wool exhibits the ability to absorb and neutralize harmful substances, including Nitrogen Dioxide, Sulphur Dioxide, and Formaldehydes, through chemosorption (thegreenage, 2017). This not only enhances its insulating properties but also contributes to a healthier interior environment. Moreover, compared to mineral wool, sheep wool accumulates less moisture on the cold side (HELEPCIUC, 2017).


In conclusion, sheep's wool fleece possesses a wide range of physical, mechanical, chemical, optical, acoustical, and physiochemical properties that make it a highly suitable material for thermal insulation. Its low density, excellent elasticity, and superior thermal conductivity make it an effective insulator, outperforming many of its alternatives. Additionally, its chemical treatment enhances its resistance to insects and moisture, further enhancing its durability. The ability to absorb and neutralize harmful substances and its sound absorption capabilities add to its appeal as a thermal insulating material. Overall, the properties of sheep's wool fleece make it a promising choice for various insulation applications.

Updated: Jan 02, 2024
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Investigating the Properties of Sheep's Wool Fleece as a Thermal Insulating Material. (2024, Jan 02). Retrieved from

Investigating the Properties of Sheep's Wool Fleece as a Thermal Insulating Material essay
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