Article on the Properties of Wool

Wool: All You Need To Know About This Natural Fiber

About Merino Wool

Wool is a natural fiber. It is composed primarily of keratin. This is a protein that is found in hair, fingernails, and animal hooves. Sheep are the main source of wool but other animals such as goats, alpaca, and llama as contribute wool. Wool grows in clumps called staples. These staples are held together by grease and lanolin in freshly shorn wool. When sheep are shorn the wool comes off and has an appearance of a blanket also called a fleece.

Wool has been around for some time. It has been used for years to make thick sweaters that were used for activities where you needed to stay warm such as polar exploration and mountain climbing. These old garments were made out of thick, scratchy, shrink prone and bulky wool. They are nothing like the wool that is used in modern sportswear today. In the 1990’s performance-wear companies started using Merino Wool sourced from New Zealand and Australia to produce their garments and socks. Merino sheep are a breed of sheep that originated centuries ago in Spain. Merino Wool is from Merino Sheep which have fibers that are finer than fibers from regular sheep. It is estimated that one square inch of skin on a merino sheep produces four times the number of fibers than other breeds. Merion sheep are raised in harsh climates where the summers are hot and the winters brutally cold. Merino Wool is a fiber that can adapt to both extremes and protects the sheep all year round.

Wool fiber has two noteworthy characteristics.

  1. Wool fibers are scaly with nibbled edges, like stacked cones on top of each other. These cones when washed with warm and soapy water would slide down on themselves and shrink. With modern advances, factories can now prewash the wool to smooth out these scales, making the wool less likely to shrink. These scales also have a major role in wool’s resistance to water.
  2. The other main characteristic of wool is that it is crimped (bends or crinkles), creating millions of little airspaces within the fibers. These air pockets are what let wool adapt so well to the changing environment.  Making it a great material for a variety of garments and socks. The high number of crimps per inch is also what gives wool a soft feel next to the skin. Wool garments also exhibit excellent shape retention due to the crimps in the wool. Lastly the abundant crimps in the wool fiber allow the spinning of high bulk, resilient yarns, which then can be knitted or woven into structures tailored to particular end uses. For outdoor apparel and socks, knits are the most common structures.

The Measurement of Wool: Microns

Wool fibers are generally measured in microns (A micron equals one millionth of a meter). The smaller the micron gauge the finer and softer the wool fiber. To give some perspective, a human hair is 60-80 microns. Old school wool sweaters were generally made out of 30-32 micron wool fibers. (This wool was scaly, scratchy, heavy, and had a tendency to shrink.) Modern Merino Wool is between 17.5 – 24 microns. The 17.5 micron wool is used in lightweight next-to-skin garments where 24 micron wool is used in outerwear garments such as sweaters. Some manufacturers will use a different metric when describing the thickness of the wool used. This measurement is grams per meter squared (g/m2). The lower the number, the lighter and thinner the garment. 

Cold Weather Performance

Wool has a history of being a great fabric for cold weather wear. Wool absorbs sweat vapor and releases it on the other side; preventing clamminess and the wet feeling against the skin. Those same air pockets mentioned above trap warm air next to the skin and insulate the body even when wet. This is very important in cold conditions and stop & go activities in cold weather. Wetness against the skin can cause conditions such as hypothermia making wool an excellent fabric for those activities.

Warm Weather Performance

Wool is also a good fabric for warm weather. As sweat evaporates from your skin it cools the skin and the nearby air. The millions of air pockets created by the crimps in the wool trap this cool air and protect you from the warmer temperatures outside. The core (cortex) of the wool fibers are hydrophilic (moisture loving) and can absorb 1/3 of their weight in water (estimates are from 27%-36%) without feeling damp. The exterior of wool fibers are hydrophobic (moisture hating). This means that while the fibers can absorb sweat, against the skin is the hydrophobic layer so your skin will feel dry even if the fabric is soaked with sweat. In this condition the fabric may feel slightly heavier than in its dry state.

Water Resistance

The scaly exterior layer of wool fiber is called the cuticle. It is overlaid with the epicuticle, itself coated with lanolin, a waxy, water shedding film. The epicuticle and its waxy coating is what creates wool’s resistance to mist and light rain. The structure also makes wool resistant to stains, mildew, and mold.

Odor Control

Wool contains lanolin which has antibacterial qualities. Since wool also absorbs water into the inside of the fiber, there is no moisture on the outside that microbes can grow on. This is what keeps wool garments from smelling. This is mainly appreciated for those around you when you have been active.


Wool has a lower propensity for ignition, and burns with a lower heat than all other textile fibers. The protein Keratin does not support combustion. While the application of flame to the fiber will initially cause some smoldering, it will not ignite. In comparing wool to synthetic fibers, wool will not melt when burned.

Wool vs. Synthetics

Synthetics tend to be lighter, cheaper, and dry quicker than wool does. Merino Wool though tends to feel warmer, fights odor, and feels less clammy when wet. Synthetic layers “wick” sweat away from your skin. To do this it transports moisture between hydrophilic fibers to the outside of the garment to evaporate. This requires sweat to condense before it is moved through the fabric – an extra step which wool proponent say makes synthetics process slower than wools moisture management system. Wool is also natural, biodegradable, and renewable. It also can be produced using less petroleum and fewer toxic chemicals than its synthetic competitors.

Accreditation: Zque

Most of the major wool brands have their products Zque certified. Zque certification is an accreditation program that ensures the integrity of the wool fiber that is sourced. The Zque program ensures environmental, social and economic sustainability, animal welfare (non-mulesed) and traceability bake to the source. Wool fibers will actually be weaker and of lower quality if the animal is exposed to high levels of stress. Icebreaker, Smartwool, Ibex, and Mapp merino all use Zque certified wool.

Care for your Wool

Modern wool garments can now mostly be washed in the washing machine. Still check the labels and follow the instructions. Most garments can be washed on a delicate cycle with cold to warm water. Use a delicate detergent made for wool or one of the detergents marked “free” or “clear”. Do not wash with bleach or with any velcros or barbs as they could damage the wool. Also, turn garment inside out to avoid color fading and abrasion. Some wool garments can be tossed in the dryer under low heat but most are best air-dried laying flat. While wool needs a little more effort to keep up, since it is antibacterial, it does not need to be washed as often as synthetic pieces.

Wool Products Reviewed

About the author

I am an avid runner, cyclist, swimmer, hiker, climber, skier and many other activities that would make this list too long. I started Your Mileage May Vary Reviews in Early 2011 to combine two of my passions: sports and gear.

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