Quick answer: for most sweaters the best yarn is merino wool at Nm 2/14 to 2/24 (DK to sport weight). It is elastic, so the sweater keeps its shape; it is soft enough for next-to-skin wear; and it pills less than cashmere or alpaca. Choose a merino-cashmere blend when softness matters more than price, alpaca when you want a heavy, warm, relaxed drape, and cotton or linen for summer.
After two generations in the Italian yarn trade we have seen every fibre, blend and weight used for sweaters. Below is what actually holds up after a season of wear, organised around the questions knitters ask us most.
Which Wool Is Best for Sweaters?
| Fibre | Holds shape | Warmth | Softness | Pilling | Best for |
|---|---|---|---|---|---|
| Merino | Excellent | High | High (16–19 micron) | Low | Fitted pullovers, cables, colourwork |
| Cashmere | Fair | Very high | Highest | High | Luxury layers, blends |
| Alpaca | Poor | Very high | High (baby alpaca) | Medium | Oversized, drapey sweaters |
| Lambswool / Shetland | Good | High | Medium | Low | Rustic, hard-wearing sweaters |
| Cotton | Poor | Low | Medium | Low | Summer sweaters |
| Silk blends | Poor | Medium | High | Low | Special-occasion knits |
Merino wins on the balance that matters for a garment you pull on and off hundreds of times: elasticity plus softness. The other fibres each beat it on one property and lose on another.
What Is the Warmest Wool for a Sweater?
Alpaca and cashmere are the warmest, and both are warmer than merino at the same weight. Cashmere achieves it with a very fine, crimped fibre that traps air; alpaca with a dense fibre that drapes heavily and blocks wind. If you want maximum warmth in a fitted shape, use a 70% merino / 30% cashmere blend so the merino keeps the fit while the cashmere adds warmth. If you want maximum warmth and do not mind a relaxed, heavy fabric, use alpaca or a 70/30 alpaca-wool blend.
What Is the Most Comfortable Wool for Sweaters?
Superfine merino, 16 to 19 micron, is the most comfortable wool for a sweater worn against the skin. Below about 19 micron the fibre ends bend rather than prick, so the "itchy wool" feeling disappears. Cashmere is softer still, but a pure cashmere sweater stretches out of shape and pills at the underarms and cuffs, which is why Italian mills sell so much of it as a blend. Alpaca is soft and lanolin-free, which suits people who react to sheep's wool.
Which Yarn Makes a Sweater That Won't Lose Its Shape?
Merino and other wools. Wool fibre has natural crimp that acts like a spring: stretch the fabric and it recovers. Alpaca, cotton, silk and linen have little or no crimp, so a sweater knitted from them grows with every wear and rarely comes back after washing. If you love the look of one of those fibres, knit it at a firmer gauge, add shaping seams, or use a blend that contains at least 30% wool.
Best Yarn by Sweater Style
- Fitted pullover or cardigan — merino or merino-cashmere, Nm 2/14 to 2/24. Elasticity keeps the fit.
- Oversized, relaxed fit — alpaca, alpaca-merino or a chunky merino, Nm 2/8 to 2/20. Drape is an advantage here.
- Cable-knit or Aran — merino, lambswool or a merino-cashmere blend, Nm 2/10 to 2/16. Cables need spring and stitch definition.
- Lightweight summer sweater — cotton-cashmere, linen-silk or a cool-wool merino, Nm 2/24 to 2/36.
- Colourwork and Fair Isle — merino or Shetland-type wool, Nm 2/24 to 2/36. Even gauge and grip between colours matter most.
How Much Yarn Do You Need for a Sweater?
For a standard adult sweater, size M:
| Weight | Nm range | Yarn needed |
|---|---|---|
| Fingering | 2/30 – 2/48 | 1,200–1,500 m |
| Sport | 2/24 – 2/28 | 1,000–1,200 m |
| DK | 2/14 – 2/20 | 800–1,000 m |
| Worsted | 2/10 – 2/14 | 700–900 m |
| Bulky | 2/6 – 2/10 | 500–700 m |
In grams, a DK adult sweater is usually 500 to 600 g. To turn a cone's Nm into metres: metres per 100 g = Nm × 100 ÷ plies, so a 2/28 cone gives 1,400 m per 100 g. Our yarn calculator does this from your own gauge and adds a confidence range, and our Nm guide explains how to read the count on any cone.
Best Nm for Sweaters on Cones
Cone yarn is spun finer than hand-knitting yarn, so most sweater knitters hold two or three ends of a 2/28 to 2/30 cone together to reach DK or sport weight. Two ends of 2/28 knit like a 4-ply; three ends knit like a light DK. This is the normal way to use cone yarn, not a workaround, and it lets you mix colours or fibres in one fabric. Cone yarn also arrives with spinning oil on it: knit and wash a swatch before you measure gauge, because the fabric blooms and changes size in the first wash.
Our Recommendations
- Best overall sweater yarn: an Italian extrafine merino at Nm 2/14 to 2/20. Zegna Baruffa, Lana Gatto and Millefili all spin lines of this type, and we stock them as original mill yarn sourced through Italian stock and destock channels. Browse wool yarns.
- Best luxury sweater yarn: a 70/30 merino-cashmere from Cariaggi or Loro Piana production. Cashmere softness with merino structure. Browse cashmere yarns or read cashmere vs merino.
- Warmest relaxed sweater: an alpaca-wool blend. See alpaca vs wool for the trade-offs.
- Best value: Italian wool blends at stock prices, typically around half the list price of the same yarn bought through retail.
For the softness question in more depth, read merino vs lambswool.