Complete Guide To Yarn: Fiber, Spin, Weight + More

For many of us, yarn pulls us in with an intrinsic magnetism. While its appeal can feel so mysterious, learning a bit about what yarn is and how it’s made only serves to deepen that connection. In this article, we’ll explore the basic language of yarn and the many choices you encounter when shopping for it, helping you understand how one yarn differs from another and what to consider when buying yarn—especially from an online yarn shop like ours.

At Purl Soho, we tend to talk about yarn for knitting and crochet, but it’s worth noting at the outset that you also use yarn for weaving, punch needle, crewel embroidery, macrame, and so much more. Whatever you’re making, learning how to choose yarn with both your heart and your head will bring your ideas to life and spark so many new ones.

Natural Fibers

All our yarns start out as beautiful natural fibers, drawn from the rich bounty of the plant and animal kingdoms and rooted in centuries-long fiber traditions. We love working with natural fibers because they are better for the planet and for the people, animals, and plants who inhabit it and because natural fibers are full of complex beauty, fascinating tactility, and endless variety.

Properties Of Natural Fibers

Every type of fiber used to make yarn has its own unique properties, some born of adaptations to survive in nature and others shaped by caring human hands. These differences can be fairly obvious, like cotton versus alpaca, or more nuanced, like Andean highland wool versus merino wool. Let’s dig into the many properties of yarn that help distinguish one from the other…

• Staple Length: The length of individual fibers before they’re spun into yarn. Staple length ranges from less than 1 inch to 8 inches or more, with shorter lengths tending to make softer, loftier yarns and longer ones spinning into smoother, stronger yarns, especially when those fibers are fairly uniform in length.

• Microns: Microns measure the diameter of individual fibers, most often used when talking about wool, cashmere, and other animal fibers. Finer fibers have a lower “micron count”—often in the 14-17 range for cashmere, for example—and tend to feel softer, while thicker fibers, like many basic wools, are generally in the 20-25 range.

• Strength + Resilience: Strength refers to how difficult a fiber is to break apart, while resilience refers to how well a fiber stands up to wear, abrasion, and pilling. Together, these qualities influence how long a yarn will look and feel good in a finished project.

• Density: Density describes how heavy a fiber is relative to its volume. Two yarns can appear the same size but feel very different in your hand because their fibers have different densities. Wool, for example, is a relatively low-density fiber, while linen and silk are much denser and often feel weightier.

• Elasticity + Crimp: Elasticity determines how springy a yarn feels and how well it returns to shape after washing, wearing, and storage. Fibers with natural crimp, like wool, are more elastic, while straighter fibers, like cotton, stretch less and recover more slowly.

• Surface Structure: Many animal fibers have microscopic overlapping scales, like shingles on a roof. The presence and prominence of these scales affect how fibers grip one another, influencing warmth, softness, sheen, drape, and a yarn’s tendency to felt.

• Insulation + Thermal Regulation: This describes how well a fiber holds heat and moderates temperature, including when it’s wet. Many properties contribute to a yarn’s warmth, but a big factor is its ability to hold air, so lofty, crimped, scaly fibers that continue to insulate even when damp (think, wool!) are most insulating.

• Absorbency: Absorbency is the ability of fibers to retain water. This determines how yarn accepts and holds dye, as well as which ones make good dishtowels and washcloths—and which don’t!

• Luster: Luster is the way a yarn reflects light, from softly matte to smooth and shiny. It’s influenced by the fiber’s crimp and surface structure, as well as how the yarn is spun.

Animal Fibers

Happy Cormo sheep at Earthstar Farm, who grow all the wool for our Big Mountain Cormo Worsted yarn | Photo courtesy of Earthstar Farm

We love our fiber-bearing friends, as much for their sweet faces and endearing personalities as for the incredibly beautiful fibers they grow. There’s a huge variety among animal fibers, especially between different species, but also between different breeds. In general, animal-fiber yarns tend to be more insulating and elastic, and less dense than plant-fiber yarns.

Our collection of animal-fiber yarns includes…

• Wool: Fiber shorn from sheep, prized for its warmth, elasticity, and versatility. The planet’s huge variety of sheep breeds offers a near-endless diversity of wool yarn, ranging from the softest extra-fine merino wool to resilient Andean highland wool and sproingy Cormo. Lightly processed wool yarns are rich in lanolin, a natural waxy coating that conditions the fibers and helps them repel water and resist odors. Wool fibers come in a range of micron counts and degrees of crimp, but all wool fibers are toasty warm—even when wet! Wool yarns are also prone to felting when machine-washed. The exception is superwash wool yarns, which are treated to smooth their scaled structure so that you can gently machine-wash them without fear of shrinkage.

• Alpaca: A very soft, low-lanolin animal fiber loved for its warmth, luster, and drape. Most alpaca yarn comes from the Huacaya breed, which grows relatively long fibers with a gently crimped structure. Be sure to explore Suri alpaca as well, an incredibly soft, silky fiber with a glowing halo that rises above the surface of the fabric. Alpaca fibers have hollow cores, allowing them to trap lots of heat, and are naturally low in lanolin, making them a good choice for people with wool sensitivities.

• Cashmere: An ultra-fine fiber combed from the undercoat of cashmere goats, valued for its exceptional softness and lightweight warmth. Made from one of the softest natural fibers in the world, cashmere yarns also have a gentle drape, a beautiful bloom that fills the spaces between stitches, and a lush, downy halo. Learn lots more about this extraordinary fiber in our article, The Ultimate Guide To Cashmere Yarn.

• Mohair: A long-staple fiber from Angora goats, known for its downiness and luster. A very strong and warm fiber, mohair has an incredible ability to absorb dye, resulting in brilliant, jewel-like colors. Mohair yarn is easy to distinguish by its luminous, cloud-like halo, which reflects light beautifully and adds softness and depth to your finished fabric.

• Silk: A smooth, continuous filament fiber produced by silkworms, prized for its strength, luster, and temperature regulation. Silk is the strongest natural fiber by weight and is best known for its incredible shine and ability to absorb luminous color. All our silk yarns are made with soft mulberry silk, produced from the cocoons of silkworms that feed exclusively on mulberry leaves.

• And More: In our collection, you’ll also find 100% baby camel yarn and pure yak yarn… True treasures with their own unique stories to tell!

Our pure merino wool Wild Donegal yarn is a real Irish tweed yarn with all the warmth, springy feel, and sheep-y goodness you expect from wool!

Plant Fibers

Soft, cooling cotton yarns, from pure cottons like Cotton Pure to yarns like Sweetgrass where cotton mingles with superfine alpaca

Classics for warm-weather knitting, plant fibers are cool to the touch, more breathable and absorbent than animal fibers, and generally denser and less elastic. Yarns made with plant fibers are usually machine-washable and easy to care for, as well as vegan-friendly and hypoallergenic.

Our collection of plant-fiber yarns includes…

• Cotton: A soft, breathable plant fiber beloved for its comfort, absorbency, and versatility. Cotton is cool and breathable—a classic fiber for hot weather—and the plant comes in countless varieties selected for softness, absorbency, or strength. We only use unmercerized cotton for our cotton yarns, which skips an avoidable chemical treatment and has a naturally soft, matte finish. Learn even more about cotton in our article, Cotton Yarn: Why We Love It (And You Will Too!).

• Linen: A strong, straight plant fiber made from the stems of the flax plant, known for its cool feel and durability. Linen is the ultimate fiber for keeping cool and absorbing water. It also has a beautiful earthy quality and a hardworking nature, and linen yarns get softer and more pliable with washing and wearing.

• And More: In our collection, you’ll also find plant-based yarns made with hemp and bamboo. Known for their durability and breathability, both are quick-growing plants that are generally less water-intensive than cotton.

Our Sketchbook Cotton yarn is made from two North American cottons… Soft, cooling, and very beautiful!

We work with amazing fiber mills all around the world to turn exceptional animal and plant fibers into yarns we truly love to knit with—and that we know you’ll love, too! We hope you’ll explore these different fibers over the course of your journey as a knitter, noticing the unique feeling of each in your hands, on your needles, and against your body.

Yarn Spin: Twist + Plies

The structure of a finished yarn, also known as its “spin,” is characterized by three factors: fiber preparation, twist, and plies. Note that a yarn’s spin is separate from its weight—a thick yarn and a thin yarn might have a similar spin!

Fiber Preparation: Worsted-Spun vs Woolen-Spun

Fiber preparation describes how fibers are organized before they’re spun into yarn, and it has a big impact on the yarn’s finished structure and properties. Most of our yarns are worsted-spun, meaning they’re made from fibers that have been combed and carefully aligned, resulting in a smoother, denser, glossier yarn with excellent stitch definition.

We also offer many woolen-spun yarns, which are spun directly from fluffy carded fiber. Woolen-spun yarns have a slightly fuzzy finish compared to worsted-spun yarns and also trap more air, making them lighter, loftier, and warmer, with a beautiful bloom!

Twist

Twist is the force that binds fibers together to create yarn. Some yarns have a lot of twist, while others have less—the fiber’s staple length and structure determine how much friction from twist is needed to hold the yarn together.

Twist is added during spinning, whether by hand or by a mill. Either way, specialized techniques and equipment apply just the right amount of twist to stabilize the fibers and produce a huge variety of yarn textures, from smooth and firm to soft and lofty.

Plies

Left to right: single-ply Partridge Superwash, 2-ply Cashmere Merino Bloom, 3-ply Yonder, and multi-ply Nigh Aran and Plenty

Plies are the individual strands of spun fiber that are twisted together to make yarn—the building blocks of yarn. Some yarns are made from a single ply, while others combine two or more plies spun together. Some are even created by spinning together multiple already-plied strands.

Each ply can be thick or thin, bumpy or perfectly even, tightly spun or loosely spun… And they can be combined and spun together in countless different ways. In general, more plies create a stronger, rounder, more durable yarn, while fewer plies often result in yarns with more softness and bloom.

It’s important to consider the number of plies when you choose a yarn for a project. Single-ply yarns are beautiful for accessories that won’t get a lot of surface wear (like hats!); two-ply yarns bloom beautifully in colorwork; and multi-ply yarns offer crisp stitch definition for cables and other textured patterns.

Our Partridge Superwash yarn is a beautiful example of a single-ply yarn, with an incredibly soft surface and radiant natural luster.

Yarn Weight

Yarn weight is a category that describes how thick a yarn is, relative to other yarns. We use the Craft Yarn Council (CYC)’s standards for yarn weight across all our yarns and knitting patterns, as do many other yarn companies and pattern writers. That said, there are other standards out there and plenty of wiggle room and gray area. Once you factor in needle size and your own knitting tension, yarn weight becomes a little more art than science, a flexible guideline rather than a rule set in stone.

Because yarn weight and gauge are so closely connected, this topic inevitably veers into gauge territory. If you’d like to go deeper, be sure to check out our All About Gauge Tutorial.

The whole range of yarn weights, starting with lace-weight Tussock going all the way to jumbo-weight Gentle Giant

Here are the standard yarn weights Purl Soho uses, in order from thinnest to thickest…

• Lace Weight: Very fine yarns that typically knit at about 8.25–10 stitches per inch. Lace-weight yarns can be worked on small needles for fine, dense fabrics or on larger needles for a light, airy, and diaphanous feel.

• Fingering Weight: Fine yarns that usually knit at about 6.75–8 stitches per inch. Fingering-weight yarns, including most sock yarns, are quite fine but still substantial and have a wide range of possible gauges. Learn more in our article, The Finer Things: Understanding Fingering-Weight Yarn.

• Sport Weight: Light midweight yarns that knit at about 5.75–6.5 stitches per inch. Sport-weight yarns make light fabrics that knit up more quickly than fingering weight. 

• DK Weight + Light Worsted Weight: Midweight yarns that typically knit at about 5.25–6 stitches per inch. Not too thick and not too thin, DK yarns are just right for almost anything you want to knit. Note that there’s some overlap with sport weight… We told you there are some gray areas! The terms DK yarn and light worsted yarn are often used interchangeably. Learn more in our article, What Is DK Yarn?

• Worsted Weight + Aran Weight: Classic midweight yarns that knit at about 4–5 stitches per inch. Cozy but not bulky yarns, worsted-weight yarns fall on the thinner end of the range, while aran-weight yarns are slightly thicker. Learn more in our article, Worsted-Weight Yarn Explained: The Complete Guide.

• Chunky/Bulky Weight: Thick yarns that knit at about 3–3.75 stitches per inch. Dreamy and cuddly, chunky/bulky-weight yarns are perfect for cold weather and snuggly knits.

• Super Bulky Weight: Extra-thick yarns that typically knit at about 1.75–2.75 stitches per inch. Even thicker and cozier than bulky, super bulky-weight yarns make lickety-split gift knits.

• Jumbo Weight: The thickest yarns, knitting at about 1.5 stitches per inch or fewer. The big softies of the yarn world, jumbo-weight yarns knit up unbelievably fast into thick, warm fabrics that can’t help but catch the eye!

When you’re choosing yarn for a knitting pattern, you’ll most often start with yarn weight, but there are so many other factors to think about! Keep in mind that two yarns labeled the same weight can behave very differently depending on fiber, spin, and plies, so weight is best thought of as a starting point, not the whole story.

Dyeing Yarn

You might assume that dyeing is always the last step in the process of making yarn, but that’s not always the case. And some of the most beautiful colors skip dyeing altogether, coming instead from the natural hues of undyed fibers themselves!

For many of our yarns, it’s actually the unspun fiber that gets dyed. Often referred to as fiber-dyed, this is where the phrase “dyed in the wool” comes from. Fiber-dyed yarns tend to have deep, blended color, without areas of undyed white. On the other hand, yarn-dyed and hand-dyed yarns, which are dyed after spinning, often have a lit-from-within quality, created by the warm white core of the yarn glowing through the color.

Dyeing Techniques + Styles

Left to right: undyed Big Mountain Cormo Worsted, heathered Nigh Aran, helix Linen Quill, tweed Spindle, hand-dyed Estuary, and printed Sunshower Cotton

Here are some of the most common dyeing styles you’ll find in our yarn collection…

• Solid: Yarns dyed a single, uniform color, either before or after spinning the fiber. Solid-dyed yarns tend to have an even appearance that highlights stitch definition and texture. To see an example, check out some of Nigh DK’s beautiful solid colors.

• Heathered or Mélange: Yarns made by mixing fibers of two or more colors together before spinning. The contrast can be subtle or more pronounced and may come from blending dyed fibers, undyed fibers, or naturally varied fiber colors. Most of our yarns are made this way because we love the depth and complexity it brings to color… Check out Knitting Yarn DK for some lovely examples!

• Tweed: Speckled yarns created by adding small bits of colored fiber into the base fiber before spinning. These bits—known as slubs, nepps, donegals, or burrs—can vary in size, color, and contrast, resulting in anything from gentle flecking to bold pops of colors. You’ll see this inspiring variety in our Irish tweed yarns, Spindle, Hedgerow, and Wild Donegal.

• Helix: Yarns made by spinning plies of different colors together to create a barber-pole effect. The plies may be dyed with any method and can be high- or low-contrast. We offer helix colors of several yarns, including Linen Quill and Daily Wool Worsted, and all of our Lovebird collection is helixed—and hand-dyed!)

• Self-Striping: Yarns dyed in repeating color sequences that form stripes as you knit or crochet. As the name suggests, self-striping yarns, like our Novella, create patterned (and sometimes surprising!) fabric without the need to change yarns.

• Hand-Dyed: Yarns dyed by hand using techniques such as kettle-dyeing, hand-painting, and speckling. This category includes a wide range of techniques, from semi-solid and tonal yarns with subtle variation to variegated yarns with high contrast and multiple colors… All present in our collection of hand-dyed yarns!

• Printed: Yarns with color applied to the surface of the finished yarn in a repeating pattern. Printed yarns may be created by a machine or by hand and often have a playful, graphic quality. Our printed yarns, like Sunshower Cotton and Fine Print, are speckled with joyful color!

Undyed Yarns

Simply Camel is one of our gorgeous undyed yarns, showcasing glorious pure baby camel fiber in all its desert glow.

Of course, not all color in yarn comes from dye at all—some of our very favorite colors come straight from nature! Our undyed yarns celebrate the natural colors of fiber, whether a pure expression of a single fiber, like our Simply Camel yarn, or a mix of two or more undyed fibers, like our Sweetgrass cotton-alpaca yarn.

Natural Fibers + Dye Uptake

Our Estuary yarn is a hand-dyed beauty, where the variations in color are highlighted by the way the three different fibers—merino wool, mulberry silk, and linen—take the dye.

A yarn’s fiber content plays a major role in how it absorbs dye. The same dye applied to merino wool, linen, and mohair can look very different because of each fiber’s absorbency, surface structure, and chemical properties. Linen Quill is a great example; made with three different fibers, each takes dye a little differently, resulting in beautifully mingled color.

Another lovely effect comes from dyeing over naturally colored, undyed fiber, where the base fiber shows through the dye as a warm undertone. Our hand-dyed Vinter Wool palette is a perfect example of gorgeous, layered color!

Yarn Put-Up

Yarn put-up refers to how yarn is packaged for sale and use. Once yarn is spun and dyed, we carefully consider how we’ll deliver it to you in a way that feels delightful in your hands. There are lots of options, and at Purl Soho our yarns most often come in skeins, balls, cakes, or cones, mostly in 25- 50-, 100-, and 1,000-gram put-ups.

Skeins, Cakes + Balls

• Skeins (or Hanks): Large loops of yarn twisted into a loose braid. We love yarn in skeins because you can really see and feel the yarn before you knit with it. You can touch more of the yarn at once, and with hand-dyed yarns, you can see how the color looks across a longer length. Remember, skeins must be wound into balls before you can knit with them!

• Cakes + Balls: Pre-wound packages of yarn that are ready to knit with right away. Cakes are yarn balls with flat tops and bottoms, the same shape you get from most yarn winders. Balls come in a few shapes: peanut balls (or loaves) are capsule-shaped, while donut (or flat) balls are gently flattened spheres, often with a visible center hole. We also offer Mini-Ball Bundles of Linen Quill and Cotton Chirp DK, collections of 25-gram yarn peanut balls meant for joyful color play. For all styles of yarn balls and cakes, we recommend pulling your yarn from the outside to avoid adding extra twist to the yarn as you work.

• Cones: Cones are designed to hold large amounts of yarn efficiently and continuously. The best way to package a LOT of yarn is to put it on a cone.

Our Knitting Yarn DK On A Cone gives you 1,000 grams of classic New Zealand merino wool to enjoy!

We offer two of our most popular yarns on cones: Knitting Yarn DK On A Cone and Cotton Pure On A Cone. Each gives you 1,000 grams of knitting joy, with only two tails to weave in at the end of your project. Cones provide uninterrupted yardage, perfect for knitting, crocheting, and weaving blankets and garments. When working from a cone, you may find it easiest to place it on a lazy Susan or on a horizontal rod, pulling from the side rather than the top to help prevent extra twist.

Choosing Your Yarn

Understanding yarn—its fiber, structure, weight, and color—gives you the confidence to make thoughtful choices, whether you’re closely following a pattern or imagining something entirely your own. If you’re selecting yarn for a specific pattern or thinking about swapping one yarn for another, our Yarn Substitution Made Easy article takes a deeper look at how fiber, spin, weight, and gauge work together.

As you knit, you’ll learn by doing, discovering which yarns work best for certain patterns and projects and which ones you personally love most. It’s a lifelong journey and one of the biggest pleasures of being a knitter. We hope this guide encourages you to explore, experiment, and find the yarns that inspire your next project!

Article written by Andrea Lotz for Purl Soho.

Looking for more inspiration? Explore all of our knitting patterns (including tons of free knitting patterns) and knitting tutorials, buy one of our many knitting kits and yarn bundles, and shop for beautiful yarn. We have over 35 gorgeous natural fiber yarns in 100’s of magnificent colors, designed to bring integrity, beauty, and joy to your next knitting project and only available at Purl Soho!