Have you ever knit a sweater that grew as you wore it? Or used a yarn that obscured the stitch pattern? If so, you’ll know how important your yarn choice is to a sweater. Here, I’ll discuss the two most important factors in choosing the right yarn for your project: fiber content and yarn construction.
Fiber Content
Fiber content is probably the first thing most knitters consider in choosing a yarn. In choosing which fibers are best suited to a project you’ll want to consider several factors: warmth, weight, drape, and softness vs. resistance to wear.
Wool
Wool can have different characteristics depending on the breed it is made from. I’ve written quite a bit on specific breeds in this blog – check out all of my breed-specific posts for more information. In general, wool is warm and lightweight relative to many other fibers. Most wools, apart from the Longwools, have a high elasticity and will retain their shape well. Wool can absorb up to 30% of its weight in water before feeling wet, and is naturally flame-retartdent.
Because superwash wool has been treated to make the fibers less grabby with each other (which is what makes it resistant to felting), it will have less elasticity and more drape than non-superwash wool. Softer wools can be prone to pilling.
Other Animal Fibers
Most non-wool animal fibers used in yarns have less elasticity than wool. Alpaca (and other camelid fibers), silk, and mohair are all great for blending with wool to add drape. However, when used alone these fibers will not retain their shape well and can grow with wear. Alpaca and mohair can add warmth and a soft halo when blended with, or carried alongside, wool in knitted garments.
Plant Fibers
Plant fibers include cotton; bast fibers such as linen, hemp, and ramie; and semi-synthetics like rayon (made from bamboo or other fibers) and tencel. All of these are great warm weather fibers. In general these fibers all lack the elasticity of wool, so they will tend to grow with wear. Bast fibers, rayons and tencel all have excellent drape, however. Choosing a blend can give you the best of both worlds.
Synthetics
Acrylic was developed as a synthetic alternative to wool and has similar properties in terms of warmth and elasticity (however, it generally doesn’t breath as well as wool). Nylon was developed to replace silk and will add strength and drape.
Yarn Construction
How a yarn is spun makes a difference in how it will knit up and wear. A yarn can be spun worsted (with fibers aligned in one direction, not to be confused with worsted weight) or woolen (with fibers aligned in all directions), or somewhere in between (semi-worsted or semi-woolen). Worsted-spun yarns are in general heavier and smoother, and they trap less air between the fibers. Woolen-spun yarns are lighter and trap more air between the fibers. On the other hand, they are less abrasion-resistant than worsted-spun yarns.
A Note on Grist
Grist is a measure of the weight of a yarn typically given in the industry as the number of yards per pound of the yarn. You can compare the grist of two yarns by looking at the number of yards in a 50 or 100 gram skein. If you are looking for a yarn to substitute for the pattern’s recommended yarn, this is a number you want to know. Using a yarn with similar grist to the one called for in a pattern will help ensure that the yarn you’re using behaves similarly when knitted up.
Twist
The amount of twist will determine how strong and resistant to wear your garment will be. Too much twist, however, will make the yarn feel hard, like rope. Choose a yarn with higher twist for high-abrasion items like socks, and one with less twist for next to skin items like cowls. Yarns for garments should be somewhere in between.
Number of Plies
The number of plies in a yarn will affect how the stitches interact with each other. A singles yarn will be relatively round, as the fibers are round. Singles yarns also tend to create a bias in the fabric. This is because the twist is in only one direction; lied yarns are plied in the opposite direction as they are spun, making the energy more balanced. Singles yarns are also weaker and less abrasion-resistant than plied yarns.
A two-ply yarn is more of an oval shape, because the energy of the plies causes them to push apart slightly. Two-ply yarns are great for colorwork or lace. In stockinette the plies will move apart to fill in the spaces. If you have choose a breed like Shetland the yarn will ‘bloom’, filling in the space and creating a slightly watercolor-like effect in the color transitions. In lace, the holes created by yarnovers will be more open.
A three- or four-ply (or more) will result in a rounder yarn, with less space between the plies. These yarns are great for making cables and textured stitches that will stand out from the fabric.
In general, the greater the number of plies, the stronger and rounder the yarn will be. (There are other special constructions like cabled and bouclé yarns that I won’t get into here.) For more examples of how ply works with cables, lace, and colorwork, check out this piece by Jillian Moreno on Modern Daily Knitting.
Making a Choice
Your choice of yarn for a sweater project will depend on what you are looking for in your garment. Do you want to wear the sweater next to your skin, or do you need it to be hard-wearing for outdoor activities? Is drape important, or do you want to show off a particular stitch pattern? There isn’t one right answer for every project, but considering all these factors will help you find the right yarn for your dream project.
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