Wool: Fibre Guide for Knitters and Crocheters

Wool is the fibre most knitting and crochet techniques were designed around, and understanding why makes a lot of pattern advice make more sense. It comes from sheep, and its defining physical trait is crimp — a natural waviness in the individual fibre that gives wool yarn real elasticity, unlike almost any plant or synthetic fibre.

Why elasticity matters more than it sounds like it should

That crimp is why a wool sweater can survive slightly uneven tension and still block into an even fabric, why ribbing in wool actually pulls in and holds its shape at a cuff, and why a wool sock heel can stretch to go on and spring back afterward. Substitute an inelastic fibre like cotton or linen into a pattern that assumes wool's stretch — particularly anything built around ribbing or negative ease — and the fit logic of the pattern can genuinely break down, not just the drape.

Warmth and next-to-skin feel

Wool traps air within its fibre structure, which is what makes it warm for its weight. The "itchiness" people associate with wool is really about fibre diameter, not wool as a category — coarser wools (often blended for durability in rugs or outerwear) have thicker fibres that can feel prickly against sensitive skin, while fine wools like Merino have a much smaller fibre diameter and are commonly comfortable worn directly against skin. If you or the recipient of a project is wool-sensitive, that's a fibre-diameter problem first, worth solving with a finer wool before ruling wool out entirely.

Care

Untreated wool felts when exposed to a combination of heat, moisture, and agitation — the same crimp that gives it elasticity is what lets the fibres interlock irreversibly under those conditions. Hand washing in cool water, or using a washing machine's dedicated wool cycle if it has one, avoids the problem. Superwash wool has been chemically treated (the fibre's outer scales smoothed or coated) specifically so it can be machine washed without felting, at some cost to its natural crimp and a somewhat different hand-feel than untreated wool.

Gauge and swatching behavior

Wool blocks — meaning a finished wool piece can be wet or steamed and reshaped, and it will hold that new shape reasonably well after drying, more so than most synthetic fibres. An unblocked wool swatch is telling you a smaller, tighter number than the fabric will actually settle into once worn and washed, so treat any pre-blocking measurement as provisional. See what gauge is and why it matters for the general mechanics of why blocking moves the number at all.

Common wool-based yarns

Plain wool, Merino (a finer, softer wool), and wool blended with acrylic (for easier care and lower cost while retaining some elasticity) or with silk (for added sheen and drape) are all common on yarn-shop shelves. See the full fibre guide for how these compare directly.

FAQ

Does wool yarn use more or less yardage than acrylic at the same weight category? Roughly comparable at the same CYC weight category, since the category is defined by gauge rather than fibre — but two specific yarns of the same nominal weight can still differ meaningfully in actual yards per gram depending on how densely each fibre is spun. Always check the specific ball band, or use the swatch-weighing mode of the Yarn Quantity Estimator for a real answer with your actual yarn.

Is all wool itchy? No — fibre diameter, not the category "wool," determines itchiness. Merino and other fine wools are commonly worn directly against skin without irritation.

Can I machine wash wool? Only if it's labeled superwash, or you're using a washing machine's dedicated wool cycle (cool water, minimal agitation, no spin-dry heat). Untreated wool run through a standard hot wash cycle will very likely felt and shrink.