Using Superwash (or Other Slippery) Yarns in Sweaters
Look, I love a slippery yarn as much as the next gal. A touch of silk, the drape of a little bamboo - these properties can bring a delicacy to our knits. But that same silkiness can get us into trouble when we knit sweaters.
Today, I’m sharing my opinions about when to expect a good result using a slippery yarn to knit a sweater - and when it’s better to pass.
Classic Colorblock (for adults) available now, and Kid's Classic (for kids) available Nov '22, both use La Bien Aimee X Mondim, a highly grippy no-superwash yarn - but are suitable for almost any fingering weight yarn.
Which yarns are slippery?
Slippery yarns don’t have texture and slide against each other easily.
Wool fibers come with scales on them, which create friction and a "grippiness" that holds your stitches in place next to each other. Wool also has crimp, a side-to-side wave that adds friction to your fiber. Yarns without these properties are more slippery and less elastic.
Included in this category are fibers like superwash yarns (the scales have either been chemically stripped off or filled in with plastics), alpaca (the scales are at a lower angle from the main shaft, creating less friction), and silk and bamboo, which have no scales.
Sweaters need structure
To stay up and keep their shape, your sweaters need structure. The garment's weight needs to be distributed in a way that supports the garment and matches your body. Without structure, the garment can lose its shape, get baggy in unexpected ways, and stretch out in the neck, body, and sleeves.
There are multiple ways to get structure into a garment. Seams are one, but you can also distribute stitch tension evenly (such as in a yoke sweater), add more tension to the stitches (such as with extensive cabling), and use naturally highly structured yarns.
Fiber matters - but it’s not the only factor
Let’s consider two very different sweaters. On one side, we have a lightweight, woolen-spun, densely cabled, and seamed pullover with set-in sleeves and picked-up trim. On the other, we have an MCN (merino, cashmere, nylon) raglan knit seamlessly in the round. The first will have so much structure it can practically walk out the door, the second will be a liquid.
To predict whether your yarn is a good choice for your pattern, consider the pattern’s weight, construction, AND fiber. At least some of these should add structure to your garment.
The more fabric, the more weight, and the more distortion. If you're knitting a smaller size, a crop top, or a sweater knit in a light gauge, you can get away with less structure. If you’re knitting a long garment, one in a heavy yarn, or a larger size, you may not be as easily able to substitute a low-structure yarn.
Yarns that are less dense for their gauge will also be lighter - woolen spun and non-superwash will always be less dense than comparative worsted spun or superwash yarns.
The Ruffle Addendum uses a sumptuous superwash / silk blend from Sweet Sparrow. This is an incredibly slippery yarn, but because the garment is cropped and sleeveless, it's lightweight. It also has lots of structure from the seamed sides and shoulders, and has a very firm i-cord neckline.
Construction
Lots of things about the way your sweater is constructed impact how it will wear over time:
Seamed garments have more structure than seamless garments
When working seamlessly, more evenly distributed increases have more functional structure than columns of increases (ex: a yoke sweater will hold its shape better than a seamless raglan, and both will hold their shape better than a seamless drop-shoulder dolman)
Shaping that matches your body will offer a more functional structure - because your own frame will support the garment. A set-in sleeve garment will keep its shape better than a drop-shoulder garment
Working at a loose gauge will reduce structure and a dense gauge will increase it (think about the fabric you get with fingering weight on size 7 needles versus DK weight on size 5 needles)
Picking up and knitting adds structure (such as necklines and seamless-set-in sleeves)
Any stitch that adds twist or tension increases structure. This includes cables and twisted ribs
Negative ease can reduce the need for structure - the friction of the garment against your body reduces the weight hanging from the top of the garment
Putting it all together
You’re going to need to make some subjective decisions when you evaluate whether or not you should use a slippery yarn for your pattern. Overall, I look for a mix of things that give me confidence the garment will keep its shape.
Example: Classic Colorblock
Fingering weight yarn in a lace pattern is very light, and I like this in a cropped silhouette - so there’s not a lot of weight on this garment. It’s seamed, and it’s a set-in sleeve, so it’s got a lot of other structure built in. Finally, the neckline is picked up and knit, giving the garment a nice foundation.
Although I’ve used a very grippy yarn for my project, in my size I would be very comfortable using superwash or another slippery yarn.
If you'd like to knit this sweater, you can find the pattern on Ravelry or Payhip!
Go Further
If you'd like to keep exploring content about yarn substitutions and properties, here are a few things you can dig into:
This post on knitting with Cormo & Corriedale
This post on yarnie lingo
Slow Knitting: A Journey from Sheep to Skein to Stitch, from Hannah Thiessen Howard, is a lovely, thoughtful meditation on different fiber types, different ways of approaching knitting around the year, and garments written for specific, special yarns. Hannah’s love of special yarns shines through, and I know I felt like I was really "getting to know" the yarns personally