Yarn substitution: from basic to advanced.
Before you do anything else, look at the pattern and examine the design carefully. Love of Knitting patterns supply information about recommended yarns that can help you select alternatives. First and foremost, look at the yarn's weight. If a pattern calls for bulky yarn (CYC #5), you're likely to run into trouble substituting a laceweight (CYC #0). It's easiest to substitute a yarn of the same weight as the recommended yarn. (1)
The fiber content of the suggested yarn may also help you select suitable alternatives. But fiber content alone won't tell you if the new yarn will work. Examine your proposed substitution closely as you read on. If you can, cut off a 6-inch length of yarn to deconstruct.
You may have heard a yarn described as "elastic" or "inelastic," or maybe you've seen words such as resilience, bounce, or memory in a yarn's description. These terms refer to the stretchiness of a particular yarn and its ability to snap back into shape after it's been stretched. It's very easy to tell whether a yarn has elasticity or not: simply take a strand of the yarn, hold a section between your hands, and gently tug. If the strand stretches and then snaps back into shape, it is elastic. If the yarn does not have any give, neither stretching nor bouncing back, it is inelastic.
Elasticity is important because yarns that have natural stretch are easier to work with. Every time you slip your needle into a loop, the yarn will stretch to let the needle In and will bounce back to Its original shape afterward. That resiliency Is especially Important when a pattern Includes a lot of texture--cables, twisted stitches, increases, and decreases require manipulating your stitches frequently.
Certain types of fiber naturally have more elasticity than others. Wool tends to be highly elastic, and some synthetic yarns also have good resilience. Silk and fibers made from plants (cotton, rayon, and linen, for example) tend to be inelastic--they won't hold their shapes as well and may remain stretched out after you've worked patterns that require stitch manipulation. Certain yarn structures also are more elastic than others. For example, plied yarns generally have more resilience than singles; chalnette yarns, which are constructed almost like knitted I-cord, also have excellent resilience; and yarns spun worsted-style, instead of woolen, also tend to be nicely elastic.
When looking for a substitute yarn, keep elasticity In mind. If the pattern features cables or twisted stitches, textural stitch patterns, or many Increases and decreases, a yarn with good elasticity will make the knitting easier and the end result look better. Less intricate patterns are more suitable for yarns with less elasticity.
Think about a sweater with large swaths of moss stitch or a pair of mittens with a beautiful cable-and-rib motif front and center. If you've worked that hard to create such beautiful stitchwork, you want those stitches to be visible, with each individual stitch looking crisp and clean. Using a yarn that produces good stitch definition can make your finished object look more professional, with more even gauge and stitches sitting firmly where they are supposed to be rather than sagging or looking sloppy.
Some yarns have a halo--a cloud of loose fibers around the individual strands of yarn. Mohair is one fiber particularly known for a halo effect, but alpaca and angora can also appear quite fuzzy. Yarns with a halo can look and feel terrific, but the fuzziness of the loose fibers tends to obscure the individual stitches: when you look at the knitted fabric, you see the haze of loose fibers rather than the stitches underneath. The same is true of highly textured yarns or yarns with beads, sequins, tufts, or other "attachments." The attached pieces will distract the eye from the stitchwork and hide stitches.
Plied yarns, on the other hand, tend to produce good stitch definition and the more plies, the more crisp and defined these yarns are. Individual pieces of fiber get firmly twisted into the strand of yarn and are held in place by the many plies so there's no halo or fuzz. Light can reflect off the different planes of the individual plies, making patterns pop even more. When you knit with yarns like this, you'll get crisp patterns with distinct individual stitches.
When considering a yarn substitution, take a good look at the elements of the pattern you'd like to make. Does the pattern include complex stitchwork or highly textured features such as cables, moss stitch, or twisted stitches? If so, a yarn that will produce good stitch definition is ideal. If the item is meant to be cozy and warm and features relatively basic stitchwork, then a yarn that produces less stitch definition may work. Don't forget to think about the yarn used in the original sample; take note if it has halo or other prominent texture and consider how much of the design's appeal comes from the appearance of the yarn.
Elasticity and stitch definition come from the yarn's construction; drape refers to a feature of the knitted fabric the yarn creates. Think about the robes of the Statue of Liberty. They ripple and flow, pooling around her, giving the illusion of movement and swing. When knitters refer to a drapey yarn, they are talking about a yarn that creates fabric with movement and swing rather than one that holds its shape and doesn't budge.
Drape is an important quality for certain kinds of knitting projects. Skirts, shawls, lace scarves, and loose-fitting cardigans with flowing fronts all look best with a certain amount of drape. Other projects such as socks, beanies, and gloves are intended to be close-fitting. Using a yarn that drapes well to make a pair of socks may lead to heartache when the socks do not cling to the leg and foot but rather end up in a pool around your ankles. Garments intended to hug the body should not be made from drapey yarns.
As with stitch definition and elasticity, whether a fabric drapes well depends on what the yarn is made of and how it was constructed. Fibers such as silk and rayon are naturally smooth and lustrous, and that slippery surface allows the finished garment to drape well. Yarns with a smooth rather than textured finish--ribbon or tape yarns, for example--are more inclined to drape, whereas textured yarns such as boucle or yarns with noticeable nap (such as chenille) tend not to drape.
Another important factor in whether a fabric will drape is how tightly or loosely the yarn is knitted. Knitting a yarn very tightly, using smaller needles than is typical (for example, size 4 needles for a worsted-weight yarn), will result in little or no drape. The stitches will be packed tightly together, with no extra space in between for them to gently move or sway. Using larger needles than is typical (such as size 8 needles for a fingering-weight yarn) will produce larger stitches with more open space between and in them. That, in turn, will create a fabric with more drape. When deciding on a yarn, look carefully to see how important drape is to the finished project, then choose fiber, construction, and gauge accordingly.
The Final Test
Once you've chosen a likely substitute, swatch generously. A big swatch (at least 8 by 8 inches) in the pattern's stitch pattern provides more information than any other source. Even before you measure for gauge, you have the chance to test the yarn's elasticity and stitch definition. You can also evaluate the swatch's drape, which is especially important if you've chosen heavier or lighter yarn. Ultimately, it's not too hard to replace one yarn for another. But there's no substitute for a good swatch if you want to love your finished project.
The next time you are pondering a yarn substitution, take a look at the pattern you'd like to make and think about these three qualities--elasticity, stitch definition, and drape--before selecting the yarn.
Generally speaking, more plies mean more stitch definition in a knitted fabric. Notice the difference between a slightly fuzzy singles yarn (brown), a smooth two-ply (rust), a smooth three-ply (gold), a fuzzy three-ply (gray), a smooth four-ply (green), and a smooth ten-ply (blue). Although the gold and gray yarns both have three plies, the gold is more tightly twisted and has no halo, producing more stitch definition. The blue yarn will produce a fabric with superlative stitch definition, since it's actually made of ten two-ply yarns twisted around each other.
(1) It's by no means impossible to switch yarn weights, especially if you factor in the fabric's drape. Swatching is crucial if you do this (see page 71).