Animal fibers are an interesting area of clothing, in no small part because of the huge variety in sources. This is true of cotton as well for those that are closely paying attention, but the floor for cotton quality tends to be good enough that people don’t have to care as much. Various wools, on the other hand, can vary immensely in their scratchiness and warmth. This can make the difference between a cozy next-to-skin sweater, and an itchy one that requires a long-sleeve protective layer. If it’s really itchy, you may even want a neckerchief or bandana to keep it off your neck. Let’s discuss the quantifiable differences between fibers, how they are processed from the animal into an actual garment, and finally, the difference between the various animal fibers commonly used.
Fiber Thickness
In general, there is one supreme statistic that can help you identify the quality of a wool, which is the coarseness. A high grade cashmere, for example, is around 15 microns thick. A wool from the Australasian Merino sheep can be as fine as 16 microns, while the Shetland sheep from Scotland only gets to 24 microns or so. But there are still some ways this number can be misleading. Most yarn spinners will give you an average number. That means that there’s some number of finer hairs, and some number of coarser hairs. In that way, it’s possible for 2 products with the same average fiber thickness to give different feels. So how do producers even determine the width of an animal hair, and sort? Let's go over the general process of turning animal hair into a usable yarn or fabric, starting with obtaining the hair from the animal.
Shearing and Classing
During the sheep shearing process, producers will grade fibers, which is called classing. This is done essentially as soon as the wool comes off the sheep (some processing called “skirting” is performed to remove greasy or knotted up sections). After shearing, the product from a single sheep is called a “fleece,” and it is balled up and passed to the classer, who actually does the grading. Classers do this by touch and visually. A classer will pull a couple tufts of the fleece out and evaluate the feel, which will correspond with the micron thickness. The other factor that can be used to sort fineness is the coarseness of the crimp. A finer fiber tends to also produce finer, smaller waves of crimping. There are other qualities that dictate wool quality which are evaluated during classing, such as tensile strength, the evenness of the crimping, length, and even the natural color of the wool. These are used when selling the raw wool, but hardly ever make it to the consumer for evaluation, so it’s less important for this overview. This classing process is the first in a series of subdivisions which mark what final fate awaits the wool. The finest wool goes to garment manufacturer, while wool which is too short, too weak, or too coarse will go to applications like carpets or bedding.
Scouring
The wool at this point is still quite dirty. It therefore undergoes cleaning to remove soil, vegetable matter, and even some of the natural oil (lanolin) in the wool. Finer fleeces often have worse yield, because the finer fibers are better at trapping dirt and lanolin. This means that after cleaning, they will weigh less than coaster wools with the same starting weight, which contributes to their cost. A wool can lose between a third and two-fifths of its starting weight during the cleaning! At this point, there are many possible routes for cleaning, which is called “scouring” in the industry. However, the common thread is that these methods must leave the wool loose and prevent felting. As anyone who has accidentally washed a wool sweater knows, agitation can easily cause wool to irreversibly bunch up into itself, shrinking the garment, or in this case, making the raw wool into felt. To do this, the wool is transported through a series of bowls without agitation. The first several bowls usually contain powerful detergents and cleaning chemicals, which remove the water soluble contaminants and excess oil. The remaining bowls are fresh water, which gently rinse the wool with each bowl until the cleaning chemicals are diluted out. The wool is then dried and beaten mechanically to remove any larger debris that did not come out with the washing steps.
Alignment into Yarn
Scouring is followed by various alignment and further mechanical cleaning processes. These differ based on whether the wool is going to become a worsted or woollen yarn. Worsted yarn is tightly wound together and kept parallel, which makes it a much finer yarn. These are typically made into flat, light, and smooth fabrics, like a suit. Woollens, on the other hand, are allowed to retain much more randomness and different fiber lengths, which results in a fuzzy halo of wool around the core of the yarn. These go on to become woven or knit garments like sweaters or coats, which take advantage of the air-trapping halo to keep the wearer warm.
Carding
Both woollens and worsteds undergo an initial alignment, called carding. Carding uses rollers covered in little wires that stick out to catch the wool. These rollers steadily untangle the wool from clumps into individual fibers. This process also aligns the fibers so that they are facing the same direction. This alignment and detangling process will additionally allow any remaining debris to fall out of the yarn-to-be. At this point, woollen and worsted yarns will split in their processing.
Woollen Yarns
Woollen yarns are actually nearly done after carding. The carded wool is allowed to gently interlock into a web, and then comes off the rollers into narrow strips called “slubbings.” These slubbings are then ready to be spun into yarn. That yarn is then used to knit into clothes, woven into a fabric like a tweed, or even felted.
Yarn is often described by "gauge" and by "ply" when knit into a garment. Gauge refers to the number of stitches per inch. A high gauge means many stitches per inch, which means a finer texture. This gives a smooth visual appearance, and typically is more formal. Conversely, a low gauge indicates a low number of stitches per inch, resulting in a more textured and casual knit. Ply is generally seen as a shorthand for thickness. In a technical sense, it describes the number of threads twisted together in the yarn. Two-ply yarns have two threads twisted together, while thicker four-ply yarns would have four threads. You rarely see one-ply, because it is much less stable. The natural twisting of a single thread of yarn practically requires a second thread, or it will develop a bias. Higher plies result in chunkier, thicker knits. So for example, a thin, formal knit that you might wear as a v-neck under a sports coat would likely be high gauge and 2 ply. A thick shawl cardigan would likely be low gauge and 4, 8, or even 12-ply.
Worsted Yarns
As for worsted yarns, the process of going from carding to yarn is a bit more involved because it is a smoother, more refined product. There are several steps to improve alignment, remove debris, and create a tighter thread, usually divided into gilling, combing, and roving. After being carded, the wool is formed into a sliver, which is like a rope of untwisted fibers. This sliver is stretched during the gilling process, which accomplishes several goals. It straightens the natural crimp of the fibers, which allows for a smoother yarn. It also further aligns the fibers, and makes the sliver into a more uniform density. After this, a combing step removes shorter fibers that have snuck in with the longer staples, and thoroughly removes any balled up fibers (nep) or lingering debris. The sliver is re-gilled to increase the fiber straightness and uniformity, before going to the roving machine. Roving is the process of turning a thick sliver into a thinner rope. This often reduces the sliver’s thickness by 40 times, nearly down to the final yarn’s thickness. After roving, the wool can be spun into a continuous strand of yarn. This spinning process tightly twists the wool fibers together to create a much smoother and finer yarn than the woolen yarns.
Other Animals
While we went over specifically wool from sheep, there are many different animals that humans have domesticated for their fur. The most commonly known, aside from sheep, is goats for cashmere. Cashmere, unfortunately, is under heavy pressure from extreme consumer demand. Demand has skyrocketed enough that meeting customer needs has steadily turned grasslands of Asia into deserts. This is for many reasons, but chief among them is the biology of the cashmere goat. A sheep can produce 3 kilograms of wool a year, but a cashmere goat can only produce about 200 grams. That is 1/15th as much wool per animal. A single sheep can produce enough wool for several sweaters. Meanwhile, it takes five to ten goats to make enough cashmere for a substantial sweater. The boom in goat herding has led to the formation of dust bowls, because goats do not only eat the green tops of grass. Instead, they eat the entire plant, roots and all. This has had a devastating effect on the water, soil, and air in those regions. Starving goats also produce worse fibers, which are significantly coarser. In fact, originally, cashmere yarn producers often exclusively dealt with cashmere from baby goats, which have the absolute finest hairs. Now, elderly starving goats are still shorn for whatever last gasp of wool they have, which are in turn spun into the cheap cashmere we see on the market now. The unfortunate truth is, if you want the luxurious, soft, and warm experience of really fine cashmere, you must pay the price. It’s simply not possible to buy the right quality of yarn for less than 60 dollars per pound (or 130 dollars per kilogram). After factoring in labor and the retail markup, a cashmere sweater that lives up to the name is going to be several hundred dollars.
Fortunately, there are also other animal fibers that are commonly prized for their softness and warmth. The camelid family is a major source of these fibers. The Bactrian camel, for example, has an extremely soft undercoat of fur. This fur is made of hollow fibers, which are excellent insulators. The finest camel hair can also reach a mere 17 microns, which makes it on par with the finest sheep’s wool. It also is shed seasonally, which means that gathering it is very sustainable. Alpacas are another source of fine fibers, often as narrow as 18 microns in diameter. The advantage of alpaca fur compared to sheep is the lack of lanolin, which can cause allergic reactions in some people (and also produces the distinctly wool smell people may associate with sweaters).
There are even extremely fine sheep's wools being developed, like Zegna Baruffa's "cashwool." Cashwool is a curated selection of extra fine merino wool, which makes it soft enough to wear next-to-skin without itching. Merino producers have gotten down to 16 microns or so, and sometimes even offer a "top capped" selection. "Top capped" wool has a maximum thickness rating rather than an average thickness rating. This means that there are no thick hairs to create an itching sensation.Also worth noting is the vicuña, native to South America like the alpaca.
Vicuna produces an even finer fiber than cashmere, with an average diameter of 12 microns. Unfortunately, the vicuña is under significant pressure like the cashmere goat, which means that it is difficult to source high quality fibers from an ethical source without paying extreme prices.