Yarn is made from fibers that fall into three broad categories: natural fibers from animals or plants, synthetic fibers derived from petroleum, and semi-synthetic fibers created by chemically processing wood pulp. The specific material determines everything about how yarn feels, how it wears, and how it behaves when you knit, crochet, or weave with it.
Animal Fibers: Protein-Based Yarn
Animal fibers are built from proteins, which is why they feel warm, absorb moisture, and smell like burning hair if you hold a flame to them. Sheep’s wool is by far the most common animal fiber in yarn, but it’s only one option in a large family.
Goats produce several distinct fibers used in yarn. Cashmere comes from the soft undercoat of cashmere goats, while mohair comes from Angora goats and is known for its halo-like fuzziness and sheen. Angora rabbits (not to be confused with Angora goats) produce an extremely lightweight, fluffy fiber that’s often blended with wool for structure. Silk, produced by silkworms, is a filament fiber rather than a short staple fiber, meaning each strand is already very long before it’s spun. Its smooth, continuous structure became the blueprint for many of today’s synthetic filament fibers.
Rarer animal fibers command high prices because the animals produce very little usable fiber. Qiviut from musk oxen, vicuña from a wild South American relative of the llama, and bison down all qualify as luxury fibers. These tend to be exceptionally fine, often in the 8 to 16 micron range. For comparison, a human hair is roughly 70 microns across. Bison fiber, after the coarse guard hairs are removed, averages about 17.8 microns and was historically described as “the warmest possessed by any quadruped save the musk-ox.” Alpaca and yak are more accessible luxury fibers that fall between everyday wool and the ultra-rare options in both price and softness.
Plant Fibers: Cellulose-Based Yarn
Plant-based yarns are made of cellulose, the structural compound in plant cell walls. Cotton dominates this category so thoroughly that it accounts for roughly 90% of all natural fiber use worldwide. Cotton fiber itself is about 90% cellulose, which gives it a smooth, breathable quality that takes dye well.
Linen yarn comes from flax, one of the oldest textile plants. It’s stronger than cotton but less elastic, which is why linen fabric wrinkles easily but holds up for decades. Hemp yarn has similar qualities: it’s durable, a bit stiff at first, and softens significantly with washing. Dried hemp contains about 40 to 50% cellulose, with the rest made up of other plant compounds that are removed during processing.
Beyond these three, yarn can be spun from ramie, jute, bamboo, and even more unusual sources like pineapple leaf fiber and kapok. These specialty plant yarns tend to appear in small-batch or artisan products rather than mainstream craft stores.
Synthetic Fibers: Petroleum-Based Yarn
Synthetic yarn starts as petrochemicals that are polymerized into long chains, then extruded through tiny holes (called spinnerets) to form continuous filaments. These filaments can be cut into short lengths to mimic the feel of natural staple fibers or left long for a smoother finish.
Polyester is the single most produced fiber on earth, accounting for 57% of total global fiber production. In yarn form, it’s strong, holds its shape through washing, and resists stretching. Acrylic yarn is made from a different polymer and was specifically designed to imitate wool. It’s lightweight, warm, machine-washable, and inexpensive, which makes it one of the most popular choices for knitting and crochet. Nylon, composed of hydrogen, nitrogen, oxygen, and carbon arranged into chains called polyamides, is the strongest of the common synthetic fibers and often shows up blended into sock yarn to prevent holes at the heel and toe.
One downside of synthetic yarns is microfiber shedding. When washed, synthetic textiles release tiny plastic fibers into wastewater. Polyester fleece fabrics shed the most, releasing an average of about 7,360 fibers per square meter per liter in a single wash cycle. Standard polyester knit fabrics shed far less, around 87 fibers under the same measurement. Nylon and acrylic shed at rates similar to standard polyester. Washing with detergent significantly increases shedding for most synthetic fabrics.
Semi-Synthetic Fibers: Regenerated Cellulose
Semi-synthetic yarns sit between natural and synthetic. They start as a natural material, usually wood pulp, but undergo heavy chemical processing to become fiber. The result is cellulose in a new form: smoother, more uniform, and often with a silk-like drape.
Rayon (also called viscose) is the oldest of these. Wood or bamboo is broken down into pulp, dissolved in caustic soda, treated with carbon disulfide to create a syrupy solution, then forced through a spinneret into an acid bath that solidifies it back into cellulose fibers. The process involves multiple chemical steps and produces significant waste.
Lyocell (often sold under the brand name Tencel) uses a simpler, cleaner method. The cellulose pulp dissolves directly in a non-toxic organic solvent, and the process recovers 99.8% of the chemicals used. No chemical transformation of the cellulose is needed, making it a more environmentally friendly alternative. Modal is another variation, typically made from beech wood pulp, and is prized for its softness and resistance to shrinking. All three of these fibers produce yarn that feels cool against the skin, drapes beautifully, and absorbs dye in rich, saturated colors.
How Fibers Become Yarn
Raw fibers don’t become yarn until they’re twisted together. Twisting is what holds the fibers in place and gives yarn its strength. Without enough twist, fibers slide apart and the yarn falls to pieces. With more twist, the yarn becomes tighter, stronger, and more resistant to pilling, though it also loses some softness.
Most single strands of yarn are spun with what’s called a Z-twist (twisted to the right). When two or more of these strands are plied together, they’re twisted in the opposite direction (S-twist) to create a balanced yarn that doesn’t bias or skew your finished fabric. This is how the vast majority of commercial knitting and crochet yarn is made. Cable yarn takes it one step further: Z-twisted singles are S-plied in pairs, then those pairs are Z-plied together again. The result is extremely durable and pill-resistant, though all that twisting means the yarn won’t feel as soft.
How to Tell What Your Yarn Is Made Of
If you have mystery yarn with no label, a simple burn test can narrow down the fiber content. Snip a small piece and hold it near a flame. Plant fibers like cotton and linen ignite immediately, continue burning after you pull them away, smell like burning paper, and leave behind a small amount of fluffy white or grey ash. Animal fibers like wool and silk shrivel away from the flame, burn slowly, put themselves out when removed from the flame, smell like burning hair, and leave a small dark bead that crumbles easily.
Synthetic fibers behave differently from both. They tend to melt rather than burn, pulling away from the flame and forming a hard plastic bead. The smell is distinctly chemical rather than organic. Blended yarns can be trickier, since they’ll show characteristics of multiple fiber types at once.
Global Production at a Glance
The fiber landscape has shifted dramatically over the past few decades. Polyester now makes up 57% of global fiber production. Cotton comes in second, with about 24.4 million tonnes produced in 2023. Wool occupies a much smaller slice of the market, with certified sustainable wool programs covering about 4.8% of global wool production, up slightly from 4.2% the year before. Recycled wool accounts for around 6% of the wool market.
For yarn buyers, this means synthetic and synthetic-blend yarns are the most widely available and affordable, cotton yarn is a solid middle ground, and pure wool or specialty animal fibers carry a premium that reflects both smaller production volumes and the cost of raising animals. Semi-synthetic options like lyocell and modal are growing in availability as manufacturers look for fibers that combine natural origins with consistent performance.