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


From aircraft interiors and speaker covers to the finest garments, wool is a versatile fibre. Thickness ranges from 10 to 50 microns and fibre length depends on the breed and age. Very fine fibres <30 microns are prized for their softness and smoothness. They are utilised in fine suits, evening wear and underwear. Denim, workwear and upholstery tend to use coarser fibres, 25-40 microns, that offer a balance of softness and durability. The heaviest fibres are used in rugs and carpets, providing durability and good resistance to wear and tear. Wool can absorb up to around one-third of its weight in water before feeling wet. Unlike many other types of fibre, wool maintains its insulating properties when wet. This unique combination is exploited in both warm and cold weather clothing. It also has exceptional wrinkle resistance as a result of its elastic recovery. It can be bent thousands of times before breaking, many more than cotton or manmade fibres. This is due to the structure of wool, which is made up of layers of spiralling microfibrils. They straighten when stretched and pull back to their original shape when the tension is removed. The age of the sheep will also affect quality. The finest and softest wool comes from lambs (lambswool). Likewise, the wool of different breeds will have unique properties that lend themselves to different types of application. Merino is the most well known and is a fine, high quality and light coloured fibre that is bulky and soft. It is also known as Cool Wool, a brand of Woolmark, Quick-Dry Merino (QDM) from CSIRO and MerinoPerform WP by Optima Max. Rambouillet yields a similar type of wool of high value. The coarsest and heaviest wool comes from breeds like Leicester, Lincoln and Cotswold. And medium-soft types come from Columbia, Suffolk, Hampshire, Corriedale and Dorset breeds. Wool staple fibres are twisted together into yarn. The preparation steps determine alignment and this affects strength and bulk. Whereas woollen yarn is produced from loosely aligned wool fibres, worsted yarn is produced from combed and aligned fibres, with the shorter staples removed. This produces a stiffer and stronger yarn. As a building insulation material, constructed as a nonwoven slab, wool is comparable to other fibrous insulating materials, such as mineral wool and calcium silicate, for thermal insulation (0.039 W/mK) and acoustic absorption. It has the added advantage of being able to absorb moisture, which can help to prevent condensation inside a building and regulate humidity, improving the indoor climate. Its inherent flame retardant properties help here, too. Sheep are sheared in the spring when they would naturally start to moult, which helps to protect them from overheating and insect attach. 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 sheep's fleece is usable for fibre production. The rest is made up of contaminated fibre, dirt and lanolin, which must all be removed.


Design properties
Cost usd/kg
8-25
Embodied energy MJ/kg
45-125
Carbon footprint kgCO2e/kg
10.4-75.8
Density kg/m3
1310
Tensile modulus GPa
2.3-3.4
Tensile strength MPa
120-180
Compressive strength MPa
136
Hardness Mohs
1
Thermal conductivity W/mK
0.54
Temperature min-max °C
-40 to 100
Thermal
insulator
Electrical
insulator