Knitting Fiber Lexicon

How to choose the right fiber for your project

When picking yarn for a new project, it's easy to stop at color and price. But fiber content matters just as much, because it determines how the finished piece behaves – both while you knit it and for years afterward. A sweater knit in alpaca will stretch and sag over time, while the same pattern knit in wool holds its shape far better.

Ask yourself a few questions before you decide: Will the garment sit against the skin, or is it outerwear? Does the pattern rely on elasticity – cables or ribbed edges that need to stay snug? Does it need to survive the washing machine, or is hand washing fine? Do you or the recipient have a wool allergy? The answers will quickly point you toward the right fiber family.

• Next to the skin (base layers, baby clothes): choose soft fibers without prickly hairs, like Merino wool or cotton.
• Outerwear and winter garments: choose warm fibers with good elasticity, like wool or wool/alpaca blends.
• Summer garments: choose cooling, breathable fibers like linen or cotton.
• Patterns with cables or ribbing: choose elastic fibers – ideally with a high wool content – so the stitch structure holds its shape.

Natural fiber vs. synthetic fiber

Yarn is generally grouped into three origins: animal-based (from animals, like wool and silk), plant-based (from plants, like cotton and linen), and synthetic (made from petroleum products, like acrylic, polyester, and nylon/polyamide). Natural fibers breathe, regulate temperature, and often feel more luxurious against the skin, but they typically cost more and need gentler washing.

Synthetic fibers are cheaper, highly durable, and usually machine-washable without shrinking. They're also a good option for knitters with wool allergies. The downside is that they breathe less well, can feel "sticky" against the skin on warm days, and aren't biodegradable. In practice, acrylic and nylon are rarely used alone for an entire garment, but they often show up in blends to add durability – especially in sock yarn.

Blend yarns: the best of multiple fibers

Many of the most popular yarns are blends, because blending lets you combine the strengths of two or more fibers. A classic example is sock yarn, which is often around 75–80% wool and 20–25% nylon. The wool provides warmth and comfort, while the nylon lets the heel and toe withstand the friction from shoes without wearing through.

Silk is often blended with mohair to tame its airy "halo" and add shine and strength, while wool and alpaca are combined to get alpaca's soft warmth without the garment losing all its elasticity. Always read the fiber content on the yarn label – the percentages tell you a lot about how the yarn will behave, even when the yarn's name doesn't spell out every fiber.

Fiber types from A to Z

See the full overview of popular yarn brands in the US and UK for more examples, yardage and gauge per weight category.

Yarn care and maintenance

Even though each fiber has its own care recommendations (see the cards above), a few general rules apply to all hand-knitted items. Always check the ball band before washing – it states the exact temperature and washing method the manufacturer recommends, and the details can vary even within the same fiber type depending on how it was processed.

• Use a wool wash without fabric softener for animal fibers – softener can break down the natural structure of wool and silk over time.
• Dry garments flat. Hanging stretches most yarn types, especially cotton and alpaca, which have little elasticity to begin with.
• Store wool against moths in breathable cotton bags, ideally with lavender or cedar, and never in sealed plastic for long periods.
• Block finished garments gently – wet blocking evens out your gauge and helps natural fibers "set" into the correct shape.

Superwash-treated yarn (commonly seen with Merino wool) is the exception to the hand-wash rule: it usually withstands machine washing on a wool cycle because the fiber surface has been treated to prevent felting. Keep in mind that the treatment can make the yarn slightly slicker to knit with and reduce its natural elasticity somewhat.