Superwash
Superwash is a treatment for wool yarn that removes the outer scales of the wool fiber, allowing the yarn to withstand regular machine washing without felting.
Explanation
Superwash treatment makes wool yarn machine-washable by either removing or coating the microscopic scales on the surface of the wool fiber that normally interlock and cause felting when wool is exposed to heat, moisture, and agitation together. This is usually done chemically (chlorine treatment) or by applying a thin polymer coating. Superwash yarn is popular for socks, baby garments, and other items that are washed often, but it loses some of the natural elasticity and loft of untreated wool, and can therefore 'grow' slightly in size over time.
Also known as: Machine-washable wool
What the treatment does
Superwash wool has been treated so the scales on the fiber are removed or coated in a thin polymer. Those scales are what make wool felt, and without them the yarn survives machine washing.
The cost is that the yarn loses some of wool’s natural spring and ability to hold shape. Superwash garments tend to grow with wear, particularly in length.
How to work around it
Expect more growth when blocking, and be cautious with long, heavy garments. For socks superwash is often still the right call — there durability and easy washing matter more than perfect shape retention.
What superwash treatment changes about knitting
Superwash wool has had its scales either stripped or coated so the fibres cannot interlock and felt. That solves the shrinking problem and creates two others that matter while you knit.
First, it has much less memory. Ribbing in superwash merino is noticeably less springy and will relax over time, so cuffs and hems benefit from smaller needles than you would otherwise use. Second, it grows when wet, sometimes a great deal, and does not entirely spring back. A superwash swatch measured before blocking will give you a gauge the garment never has. Neither is a reason to avoid superwash — it is the sensible choice for baby garments and socks — but both are reasons to block the swatch.
Common mistakes
- Knitting a long, heavy garment in superwash without allowing for growth.
- Hanging superwash to dry after washing.
Keywords
- superwash
- machine washable wool
- superwash wool
Frequently asked questions
Can superwash really go in the machine?
Yes, on a wool cycle at low temperature and low spin. But hand washing extends its life regardless.
Why does superwash stretch more than regular wool?
Because the treatment removes the scales that give the fiber grip and spring. Without them the yarn has less ability to recover.
Is superwash wool actually machine washable?
It survives machine washing far better than untreated wool, but 'will not felt' is not the same as 'will not stretch'. A superwash garment agitated in a machine and then tumbled can come out longer and wider. Washing on a wool cycle and drying flat is the safe reading of the label.