Wool

8-25 usd/kg
Circularity potential
Very high
Strength
High
Production energy
Very high
Stiffness
Low
Embodied CO2
Extreme
Density
Medium

Wool and hair are insulating and protective in nature. For millennia, these qualities have been transferred to clothing, interiors and construction in the form of woven, knitted and nonwoven fabrics. Ranging from coarse to fine, soft to stiff and curly to straight, wool and hair have many desirable properties. For example, water resistance, moisture absorption, fire resistance (it self-extinguishes) and natural colour variation.

These fibres are made up of keratin, a fibrous protein. It is the key structural material in scales, feathers, horns and claws, as well as wool and hair. It becomes softer and more flexible when wet, losing some of its strength. This returns when the fibre dries, but means these fibres are vulnerable to certain types of environment and washing. An advantage of this weakness is that wool can be felted into dense fabric that dries to form a tough and insulating structure.

Animal fibres account for only around 1.5% of global textile production, and wool from sheared sheep dominates this (1.3%). There are many other types of hair used in much smaller quantities worldwide, such as goat (cashmere and mohair), rabbit (angora), camel, llama, alpaca, vicuña, guanaco, quiviut (muskox) and yak.

The high carbon footprint of wool fibre production is dominated in part by rearing sheep and the associated feed and methane production. Methane is a more potent greenhouse gas than CO2 and therefore gives a higher contribution to climate impact per kg. Scouring (washing) is energy and water intensive. Only around half of a fleece is usable for fibre production. The rest is made up of contaminated fibre, dirt and lanolin, which must all be removed.

Sheep are sheared in the spring when they would naturally start to moult, which helps to protect them from overheating and insect attach. There are several synthetic fibres that offer an animal-free alternative to wool. The most common are acrylic fibre, produced from polyacrylonitrile (PAN), and regenerated cellulose fibres such as acetate, viscose and lyocell.

There isn’t a lot of data for other types of hair, but it can be assumed these will not be better, because the fibre yield per animal will be less than for sheep. However, farming practices vary greatly and may be less intensive, more humane and inherently organic.

Aside from the significant environmental impacts of production, wool has many advantages in use. It is biodegradable, compostable and plastic-free, so fully circular by nature (as long as it is not full of chemical enhancements). It does not produce microplastics like synthetic fibres, which are becoming a significant problem in the environment. And in use it can be argued that wool doesn’t need as much washing, and outlasts synthetics equivalents in garments and flooring alike.


Sustainability concerns
Raw material generates polluting by-products
Sourced from animals


Goat hair includes cashmere and mohair (from the angora goat). While they are both generally considered superior to sheep wool, cashmere is softest. Obtained from the neck region of the undercoat of the cashmere goat, it is very fine and typically no more than 15-18 microns, which is comparable to the finest Merino. The highest quality fibres are obtained by hand combing the animal during the moulting period, making this an expensive fibre. It is very soft but not very strong. It is used in very fine apparel and interior textiles. Pashmina are shawls traditionally made with cashmere.

The fleece does not contain lanolin, which makes it hypoallergenic. However, it does contain natural oils to help protect it from weathering, which means scouring (washing) is required to make the fleece useable as textile fibre.


Design properties
Cost usd/kg
120
Carbon footprint kgCO2e/kg
120-160
Density kg/m3
1300
Tensile modulus GPa
1.3-1.6
Tensile strength MPa
32.5
Hardness Mohs
1
Temperature min-max °C
-40 to 100
Thermal
insulator
Electrical
insulator