The Merino wool fibre is renowned for comfort, softness, strength, versatility and technical benefits. The wool fibre is a natural protein fibre that is used in luxury fashion, high-performance activewear, accessories and interiors. The wool fibre’s internal structures work as one to create a soft, breathable, durable fibre capable of odour control, moisture management and thermoregulation.
Wool Fibre Diameter
The wool fibre’s diameter refers to the thickness or width of a wool fibre. Merino wool’s comfort comes from its smaller fibre diameter, which is measured in microns, where one micron is equal to one millionth of a metre.
Merino wool fibre diameter typically ranges from less than 17.5 microns to around 22-24 microns. Finer fibres, generally below about 19.5 microns, are prized for next-to-skin garments such as base-layers and fine knitwear due to their softness. Medium-range fibres, around 19.5 to 22 microns, are commonly used in apparel including knitwear and outerwear. Broader fibres above this range are less common in apparel and are more often used in interior textile applications such as carpets and rugs.
The wool fibre performs across a range of products, from fashion to interiors and beyond. The right micron count can help to match the right fibre diameter to the right function for optimum performance.
The Wool Fibre Structure
The structure of the wool fibre can be divided into several elements, including the cuticle and cortex layers, as well as substructures including the cortical cell and cell membrane complex, macro- and microfibrils and the matrix. Each of these elements contribute to the wool fibre’s performance from regulating temperature to odour resistance, softness and natural elasticity.
Each year, sheep produce a new fleece which is shorn seasonally. Wool is made of the proteins, lipids and minerals naturally absorbed and biologically synthesised through a sheep’s diet, with the fibre made of about 97% protein and 2-3% lipid material. Merino wool is chemically and structurally much like the hair found on other animals, but the fibre’s fineness, crimp structure, outer and inner fibre structure provide comfort, durability, elasticity, wrinkle recovery and ability to manage moisture and odour.
The Layers of the Wool Fibre
Cuticle
The cuticle is the wool fibre’s outer shell. This protective layer is made from overlapping scales that sit in a stacked formation like roof shingles. These scales guard the cortex underneath to repel moisture like light rain.
The hydrophobic nature of wool’s cuticular scales prevent moisture and liquids from seeping deeper into the fibre. While the wool fibre overall is not water-repellent, this hydrophobic capability assists with wool’s natural stain resistance. The wool fibre is also naturally hydroscopic, meaning that the fibre has the natural ability to retain moisture vapour and absorb dye, as molecules can penetrate between the edges of the scales, helping the fibre to have a good uptake of colour.
Cortex
The cortex makes up the bulk of the wool fibre. Sitting beneath the cuticle, the cortex is made from two different cell types: the orthocortex and the paracortex. These cell types grow side by side, but at different rates, to create a natural bend in the fibre known as crimp.
The crimp, or waviness, of the wool fibre is what gives wool fabric part of its breathability and temperature management qualities, as well as playing a part in softness and comfort. The crimp structure helps to trap static air between the skin and the wool fabric, creating a microclimate next to the skin to naturally maintain temperature. This not only keeps skin free from uncomfortable sweat but also insulates from cold weather and provides evaporative cooling in hot weather.
The elasticity of the wool fibre is also contributed to by the wool fibre’s crimp, which allows the fibre to stretch and recover without breaking. This spring-like quality also helps wool fabrics to resist wrinkles and maintain shape.
The Cortical Cell and Cell Membrane Complex
Inside the protective casing of the cell membrane complex is a structure called the cortical cell, which gives Merino wool its strength, abrasion resistance and durability. The cortical cell is made from a crystal-like structure, called the crystalline region, which has a highly ordered molecular arrangement that looks like crystals. This gives the wool fibre mechanical properties that include the ability to withstand bending or stretching as well as structural integrity under strain.
Sitting alongside the crystalline region is another area called the non-crystalline region. Unlike its neighbour, the non-crystalline region is less organised in its molecular arrangement, and is responsible for the flexibility of the fibre.
The non-crystalline region is also high in sulphur, which can help to absorb dyes to give longer lasting colours that don’t bleed when washed or fade over time. The cell membrane complex is also a transport channel for moisture, oils and dye molecules to pass through the wool fibre, making it a strong, flexible, breathable, easy to colour fibre.
Macrofibrils and Microfibrils
Inside the wool fibre’s cortex, keratin proteins are organised into bundles called macrofibrils and microfibrils. These look like tightly wound ropes made of many smaller strands, which gives the wool fibre its tensile strength and flexibility.
These keratin molecules provide elasticity and wrinkle recovery because of their spiralled helix shape, which helps wool fabrics to recover quickly from being folded or compressed. In particular, microfibrils help the fibre to bend and recover repeatedly - bouncing back like a spring - without damaging the integrity of the wool fibre.
Matrix
The Merino wool fibre’s matrix is the non-crystalline region found deep inside the fibre. It’s made from high-sulphur proteins with special properties that allow them to absorb moisture and odours. The matrix has hygroscopic properties, which means it can absorb and retain liquid moisture, including sweat and moisture vapour from areas of high humidity next to the skin.
The high-sulphur proteins in the matrix can capture odour-causing molecules generated by sweat. This action creates a natural odour-control mechanism that maintains a fresh wear even after long periods. When sweat on the skin releases odour-forming molecules, these molecules can migrate into the wool fibre and attach to polar amino acids in the matrix. These odour molecules are held by the wool fibre until being released in the next wash.
FAQs
What is the wool fibre?
Wool is a natural fibre grown by sheep. Each fibre is made from complex layers that work together to make wool naturally soft, breathable, durable, odour-resistant and thermoregulating.
Where does wool come from?
Wool comes from the fleece of sheep, which is shorn seasonally. Each year, sheep naturally grow a new fleece, making the wool fibre a renewable resource.
What is wool made of?
Wool is primarily made from keratin, a natural protein also found in human hair and nails. It also contains lipids and minerals absorbed through the sheep’s diet.
What kind of fibre is wool?
Wool is a natural, protein-based animal fibre. Unlike synthetic fibres, wool is biodegradable and renewable, with performance properties including breathability, temperature management, elasticity, odour management and moisture management.
What protein is in the wool fibre?
The main protein in wool is keratin. The helix-shaped molecular structure of keratin helps to give wool its elasticity, strength and resilience.
What makes the wool fibre strong?
The wool fibre’s strength comes from its inner structure, especially the crystalline regions of the cortical cells and bundles of keratin proteins in the macrofibrils and microfibrils. These give wool high tensile strength and durability.
How does wool keep me warm?
Wool fibres have a natural crimp, which traps tiny pockets of air next to the skin. This creates an insulating layer that helps to maintain body temperature, keeping you warm in cold weather, and cool in the heat.
GLOSSARY
Wool fibre diameter: The thickness or width of a wool fibre, measured in microns (one millionth of a metre). Merino wool ranges from below 20.5 micron to above 22.6 micron.;
Micron (μm): A unit of measurement equal to one millionth of a metre, used to measure fibre diameter.
Cuticle: The outer shell of the wool fibre, made from overlapping scales.
Cortex: Located beneath the cuticle.
Crimp: The natural waviness of wool fibres.
Cortical Cell: A structure inside the cortex that provides strength and durability.
Cell Membrane Complex (CMC): A transport channel surrounding cortical cells.
Macrofibrils: Large keratin protein bundles inside the cortex.
Microfibrils: Smaller keratin bundles within macrofibrils.
Keratin: A fibrous protein.
Matrix: The non-crystalline protein region deep inside the fibre.
Hygroscopic: The ability to absorb and retain moisture vapour.
Odour Control: A natural property of the wool fibre.
Tensile Strength: The ability of a fibre to resist breaking when stretched.
About this content
This content has been developed using Woolmark information about Merino wool fibre structure.