What felts
Any yarn spun from untreated animal fibre. That means:
- 100% wool that is not labelled superwash — the more rustic and less tightly spun, the faster it felts. Icelandic wool and Shetland felt fastest; a tightly plied merino felts more slowly but still felts.
- Wool blended with mohair — the mohair adds a halo and speeds the felt. Brown Sheep Lamb's Pride, 85% wool and 15% mohair, is the yarn most felting patterns are written for.
- Wool blended with alpaca, llama, camel or yak — animal fibres all carry scales, and the blend felts as long as the wool content is high.
- Single-ply and loosely spun yarns — Malabrigo Worsted, Lopi, Kureyon — which have more fibre surface exposed.
What will not felt
- Superwash wool. The treatment that makes it washable is exactly what stops it locking. No amount of hot water will felt it.
- Cotton, linen, hemp, bamboo, silk. Plant fibres and silk have no scales.
- Acrylic, nylon, polyester.
- Blends with more than about 20% of any of the above: the non-felting fibre holds the wool fibres apart, and the result is patchy at best.
A yarn that felts is marked Felting on its page here, and the felting listing collects every one we stock.
How much it shrinks
Expect the knitted piece to lose roughly a quarter to a third of its length and a fifth to a quarter of its width — length shrinks more than width, because stitches are taller than they are wide. Colour matters too: white and very pale wools are often bleached in processing and felt less readily; dark colours felt fastest. The pattern will have allowed for all of this in its pre-felting dimensions, which is why a felted bag looks absurdly large on the needles.
Test first
Knit a 6" square in the yarn and colours you plan to use, measure it, and felt it the way you will felt the piece: hot wash, a little soap, a pair of jeans in the machine for agitation, checked every five minutes. Measure again. The two numbers give you the shrinkage for that yarn, that colour and that machine, and are worth more than any table.
Felting by hand
A washing machine is fastest, but a sink works: hot water, a squirt of dish soap, and rub the piece against itself or a washboard until the stitches disappear. Shock it in cold water between rounds. It takes twenty minutes to an hour and gives more control over a piece that needs to fit — slippers, a hat.