Blocking Superwash Wool

Superwash blocking is not harder than ordinary blocking; it is just less forgiving of a swatch you did not wash. The whole problem is the gap between an unblocked swatch and a washed garment.

Why superwash grows

Untreated wool fibers are covered in overlapping scales that grip each other slightly. That grip is what stops a wet fabric sagging under its own weight - the stitches hold their neighbors in place.

The superwash process strips or coats those scales so that they cannot lock together and felt, which is the point. It also removes the grip. A wet superwash fabric has much less internal friction, so gravity does more, and the fabric lengthens. When it dries in the stretched position, it largely stays there.

The mechanism is set out in more detail in superwash vs non-superwash.

How to swatch superwash properly

This is the part that decides whether the garment fits, and it is where the extra care goes.

1. Knit a swatch at least 6 x 6 inches in the pattern stitch. Bigger than you think, so edge distortion does not contaminate the measurement.
2. Measure it dry and unblocked, and write that down. You will want the comparison.
3. Soak it for at least 20 minutes in cool water with a little wool wash, the same way you will wash the garment.
4. Squeeze out water without wringing, roll in a towel, press.
5. Lay it flat without stretching it and let it dry completely. Do not pin it to size - you want to see what it does on its own.
6. Measure again. The difference between the two numbers is your growth factor, and it is a real property of this yarn at this gauge.

If the swatch grew meaningfully in length, the garment will grow more, because it is heavier and gravity has more to work with.

Designing around the growth

• Knit the body and sleeves shorter than the pattern's finished length, in proportion to your measured growth, and let the first wash bring them to length.
• Prefer top-down construction where you can try it on and stop knitting when the length is right - though remember it will still grow after the first wash.
• Choose stitch patterns with structure. Ribbing, cables and textured stitches resist growth better than plain stockinette.
• Avoid heavy superwash for long garments. A long superwash cardigan carries a lot of weight over a lot of length, which is the worst case for this failure.
• Consider a blend. Superwash blended with nylon or a little acrylic recovers noticeably better than pure superwash.

How to block, step by step

1. Soak in cool water with wool wash for 20 minutes. Do not agitate - superwash will not felt, but agitation still distorts.
2. Squeeze, do not wring. Support the weight of the wet fabric with both hands; a wet superwash garment stretches under its own weight while you carry it.
3. Roll in a towel and press to get most of the water out. The wetter it goes onto the mat, the more it will grow.
4. Lay flat on blocking mats and pat to the measurements you want. Pin only lightly, and only where you need a shape held.
5. Do not stretch to size. With untreated wool, stretching to size is normal and the fiber recovers. With superwash it is close to permanent, so put the fabric where you want it rather than pulling it there.
6. Dry completely before moving it. A gridded mat set makes squaring a piece far easier.

Gridded interlocking foam mats are the right tool - our blocking mat picks go through what to look for.

Steam blocking superwash

Steam works and is faster, and it is the sensible choice for small adjustments and for setting a hem or a button band. Hold the iron above the fabric and let the steam do the work; do not press the plate onto the surface, which will flatten and glaze the stitches.

Steam is less thorough than a full soak - it will not even out uneven tension the way a wet block does - so use it for touch-ups rather than for the first block of a garment.

If it has already grown

Rewash and dry flat without stretching, and you will often recover part of the length - not all of it. Some superwash yarns return more than others and there is no way to know in advance except by having swatched.

If it has grown badly and will not come back, the honest options are to reblock shorter and accept an imperfect result, to reknit the affected section, or to treat the garment as it now is. That is a real cost of superwash, and it is the reason we would use untreated wool for a fitted garment you will hand wash anyway - see acrylic vs wool for where each fiber earns its place.