Yarn is made from fibers that are twisted or spun together into a continuous strand. Those fibers fall into three broad categories: natural fibers from animals or plants, synthetic fibers manufactured from petroleum-based chemicals, and regenerated fibers made by dissolving natural materials (like wood pulp) and extruding them into new filaments. Synthetic fibers account for nearly 46% of the global yarn market, while cotton yarn alone holds about 38% market share.
Animal Fibers
The most familiar animal fiber is sheep’s wool. Wool fibers are made of keratin, the same protein found in human hair and fingernails. Each fiber has a natural crimp and a scaly outer surface that traps air, giving wool its insulating warmth and springy texture. Merino sheep produce especially fine wool, prized for softness against the skin.
Alpaca fiber shares wool’s protein structure but offers better thermal insulation and a higher heat transfer rate, meaning it regulates temperature more efficiently. Alpaca yarn is also smoother than sheep’s wool, which makes it less likely to feel itchy. Mohair comes from Angora goats (not to be confused with Angora rabbits, which produce angora fiber), and its long, lustrous fibers add sheen and halo to yarn.
At the luxury end, cashmere comes from the soft undercoat of cashmere goats, combed out by hand during spring molting. Qiviut, harvested from musk oxen, is one of the rarest fibers on the planet. It’s comparable to cashmere in softness but warmer, and yarn made from qiviut sells for up to $90 per ounce. Silk stands apart from all other animal fibers because it comes from an insect: the silkworm spins a cocoon of continuous protein filament that can be unwound and twisted into an exceptionally strong, glossy yarn.
Plant Fibers
Cotton is the dominant plant fiber in yarn production. Each cotton fiber is a single cell that grows from the surface of a cottonseed, forming a hollow tube made almost entirely of cellulose. After harvesting, these fibers are cleaned, carded (combed into alignment), and spun into yarn. Cotton yarn is breathable, absorbent, and holds dye well, which is why it’s the go-to choice for warm-weather garments and everyday basics.
Linen comes from the stems of the flax plant. The usable fibers sit inside the woody stalk and must be separated through a process called retting, where the plant material soaks until the outer layers break down. The resulting fibers are longer and stiffer than cotton, producing a yarn that feels crisp at first but softens dramatically with washing. Linen is stronger when wet than when dry, which is unusual among natural fibers.
Hemp and bamboo are also cellulose-based plant fibers. Hemp processing resembles linen production: the bast fibers inside the stalk are separated, softened, and spun. Bamboo yarn, on the other hand, typically undergoes heavy chemical processing. The bamboo stalks are soaked, softened with alkaline solutions, bleached in multiple stages, and mechanically separated into fiber form before spinning. Despite its “natural” reputation, most bamboo yarn on store shelves is closer to a regenerated fiber than a minimally processed plant fiber.
Synthetic Fibers
Synthetic yarns start as chemical compounds derived from petroleum. The three most common are polyester, nylon, and acrylic, and each begins as a liquid polymer that gets forced through tiny holes (called a spinneret) to form filaments, similar to how a pasta maker extrudes noodles.
Acrylic fiber is made from a polymer called polyacrylonitrile. To qualify as “acrylic” in the United States, the fiber must contain at least 85% of this base chemical. The polymer is dissolved in a solvent, pushed through the spinneret, and then either hardened in a liquid bath (wet spinning) or dried in a stream of heated gas (dry spinning). After forming, the filaments are washed, stretched, dried, and crimped to mimic the texture of natural wool. The result is a lightweight, machine-washable yarn that resists moths and mildew but doesn’t breathe as well as animal fibers.
Polyester yarn follows a similar extrusion process but uses a different polymer, producing filaments that are exceptionally strong, quick-drying, and resistant to stretching. Nylon, the first fully synthetic fiber ever created, is known for its elasticity and abrasion resistance, which is why it shows up in sock yarn and activewear blends.
Regenerated Fibers
Regenerated fibers sit between natural and synthetic. They start with a natural raw material, usually wood pulp from trees like beech or eucalyptus, but the cellulose is chemically dissolved and then re-formed into new filaments. Rayon (including viscose) and modal are classic examples. Lyocell, often sold under the brand name Tencel, uses a closed-loop solvent process that recycles the chemicals involved, making it a more environmentally friendly option. These fibers produce yarns with a silky drape and good moisture absorption. Regenerated fibers are currently the fastest-growing segment of the yarn market, expanding at roughly 6.8% per year.
How Fibers Become Yarn
Regardless of the raw material, turning loose fibers into yarn requires twist. Twist is what holds the individual fibers together and gives yarn its strength. The two most common industrial methods are ring spinning and open-end (rotor) spinning.
Ring spinning feeds a thin ribbon of aligned fibers through a set of rollers that draft (thin out) the ribbon, then passes it through a small ring on a rapidly rotating spindle. The rotation inserts twist, locking the fibers together. Ring-spun yarn tends to be smoother, stronger, and softer because the fibers are well-aligned before twisting.
Open-end spinning skips the drafting rollers. Instead, individual fibers are fed into a high-speed rotor that whips them into a yarn in one step. It’s much faster and cheaper than ring spinning, but the resulting yarn is bulkier and slightly less uniform. Most budget cotton yarns for crafting use this method.
After spinning, yarn can be plied, meaning two or more single strands are twisted together. Plying adds strength, balances out the twist so the yarn doesn’t curl, and creates a rounder, more even strand. A “2-ply” yarn is two singles twisted together; a “4-ply” is four. More plies generally mean a sturdier, denser yarn.
Fiber Blends
Many yarns combine two or more fiber types to capture the best qualities of each. A classic example is sock yarn blended from roughly 75% wool and 25% nylon. The wool provides warmth and cushion while the nylon adds durability and prevents holes at the heel and toe. Cotton-polyester blends pair cotton’s breathability with polyester’s wrinkle resistance and shape retention.
Plant-fiber blends are gaining ground too. Research into flax-cotton blends found that a ratio of about 25% flax to 75% cotton produced the best overall yarn quality, combining linen’s strength with cotton’s softness and ease of spinning. These blends also appeal to sustainability-minded buyers because flax requires less water and fewer pesticides than cotton alone.
Some newer yarns incorporate recycled materials. Companies now collect plastic waste from coastal areas, shred and melt it down, and extrude it into polyester filaments that get spun into yarn. The resulting fiber performs identically to virgin polyester but diverts plastic from oceans and landfills.
Yarn Weight Categories
Once you know what a yarn is made of, the next thing that matters is its thickness, called yarn weight. The Craft Yarn Council maintains a standardized system with eight categories, ranging from lace (the thinnest, producing 33 to 40 knit stitches per 4 inches) to jumbo (the thickest, at 6 stitches or fewer per 4 inches). The most popular weight for general knitting and crochet is “medium,” which includes worsted and Aran-weight yarns and knits at about 16 to 20 stitches per 4 inches on size 7 to 9 needles.
Yarn weight is independent of fiber content. You can find a lace-weight yarn in cashmere and a bulky yarn in acrylic, or vice versa. The weight tells you how thick the strand is and what kind of fabric it will produce; the fiber content tells you how that fabric will feel, wear, and care for over time.