What is superwash wool and why does it behave differently?
Superwash wool has had its scales chemically stripped or sealed under a polymer, so it cannot felt. It also stretches more, dries slower and behaves like a different fibre in every way that matters.
- Difficulty
- beginner
- Time
- 8 min
- Read
- 3 min
Short answer
Superwash wool is wool that has been treated — usually chlorinated to erode the scales, then coated in a thin polymer — so the scales can no longer ratchet into each other. That makes it machine washable. It also makes it heavier when wet, slower to dry, more prone to growing in length, and less able to hold a blocked shape. Wash it cool on a gentle cycle and dry it flat anyway.
Machine washable wool is not a marketing claim, it is a process, and the process changes the fibre in ways that go well beyond the wash. Knitters meet this first, because a superwash yarn behaves differently on the needles, but anyone buying wool clothing benefits from knowing what the label means.
Step by step
- Know what the treatment does.The most common route is the Hercosett process: a chlorine treatment partly dissolves the scale edges, then a thin cationic polymer resin is applied that fills in and smooths what is left. The fibre can no longer catch on itself.
- Understand what that buys you.The garment can be machine washed without felting. That is genuinely useful for children's clothes, socks, base layers and anything that will be washed by someone who will not read a label.
- Understand what it costs.Superwash wool absorbs and holds more water, so it is heavier wet and slower to dry. It has less friction between fibres, so it stretches more readily under its own weight and recovers less. Blocking it holds less well, so a shape you set will drift back.
- Adjust the drying, not the washing.Because it grows when wet and heavy, superwash knitwear must still be dried flat and reshaped. Hanging a wet superwash jumper is how you end up with a knee-length one.
- Still wash it cool and gentle.The treatment prevents felting; it does not make wool indifferent to heat. Hot water and hard agitation still damage the fibre, fade the dye and wear the garment out faster.
- Read the label rather than guessing.Terms you will see: superwash, machine washable wool, total easy care, and the Woolmark machine wash symbol. Wool with no such claim should be treated as hand wash only.
Tips
- Superwash yarn takes dye more intensely and more evenly, which is why hand-dyed sock yarns are almost always superwash and why the colours look so saturated.
- Socks are the strongest case for superwash: they are washed constantly, they need to survive it, and nobody hand washes socks.
- If a superwash jumper has grown, wash it again and dry it flat — the growth is stretch under wet weight rather than permanent damage, and it can often be reset.
- Non-superwash wool is the better choice where you want the garment to hold a shape you have blocked into it, such as lace, cables and colourwork.
Common mistakes
- Tumble drying superwash wool because the label allows a wash — Machine washable rarely means tumble dryable. Heat plus tumbling shrinks and hardens the fibre even when it cannot felt.
- Hanging superwash knitwear to dry — It holds far more water than untreated wool and the weight pulls the fabric down permanently in that wet state. Dry flat.
Questions people ask
Is superwash wool still wool?
Yes. It is the same keratin fibre with a modified surface. It insulates, breathes and resists odour in the same way, and it is still damaged by heat and by biological detergent.
Can I superwash-treat wool at home?
No. It is an industrial chlorination and resin process, and there is no domestic equivalent.
Is it less environmentally sound?
The chlorine-Hercosett route has a real effluent burden, and some producers now use alternative enzyme or plasma treatments. If it matters to you, look for a named alternative process rather than the generic superwash claim.