The article is A Guide to Yarn Substitution by Jody Pirrello and is located at Knotions, a new website I found through Ravelry today.
These are a few things that it had to say:
100% wool yarns have a good resiliency and retain their shape well. They are also very absorbent – making wool a great choice for garments that will be worn outside in the harsh elements. Due to its loft, wool yarn tends to be lighter in weight than other animal- and plant-fibers.
If the garment was made with a particular breed of sheep – e.g. Merino or Shetland – keep this in mind too. The short staple, smoothness of a merino or the long staple, grabbiness of a Shetland yarn will also play an important role in your substitution.
Sometimes called “poor man’s cashmere”, alpaca is a soft fiber, weightier than wool and with a beautiful drape. This drape also translates to a lack of elasticity – ribbing and cables will flatten out because alpaca doesn’t retain its shape well. Alpaca is also known for its warmth – the hollow core of alpaca fiber makes it very insulating and much warmer than a garment made of wool.
Known as one of the most luxurious fibers, cashmere is super-soft fiber with great insulating properties. Similar to alpaca, cashmere has a lovely drape and lacks elasticity – ribbing and cables won’t stand up in a cashmere yarn. Its short staple length – the length of the fiber before spinning – makes it susceptible to pilling as well.
Like most plant-based fibers, cotton is a non-insulating fiber with a much greater weight than its animal-based counterparts. Garments made in cotton will weigh more than garments made in a wool. If you’re in a warmer climate and looking for a substitute for wool, consider a blend instead to give you the coolness of cotton without all the weight.
Linen and Hemp
As with cotton, linen and hemp are warmer weather yarns that lack elasticity. These fibers are lighter in weight than cotton though, and they also have a lovely drape. Linen and hemp yarns are typically wet spun, giving them an almost string-like feel when knitting it up. Some knitters find the texture of these fibers to be very hard on their hands and wrists, so try out a hank before committing to a whole project. One of my favorite FOs is a linen skirt I made last year and I found the effort outweighs the final product – after wearing it I just drop it in the hamper and wash and dry it like I do my jeans and t-shirts. With each wash and dry the yarn fluffs up and softens beautifully.
Bamboo is an absorbent fiber with a high sheen, and a drapey silkiness. It tends to be a heavier fiber, and garments may benefit from using this fiber as part of a blend. Scarves, stoles and wraps are excellent choices for bamboo when it’s not paired with another fiber.
Another warm weather alternative, soy yarns have high sheen and great drape. As you may have noticed by now, great drape is often at the price of elasticity, and soy yarns tend to be inelastic.
Selecting a Suitable Substitution
Now that you have the basics outlined for you – gauge, fiber, weight, and ply – you may find several options worth considering. You know what’s coming next, right? Swatch, swatch, swatch.
Knit up a good-sized swatch (at least 3-4 inches wide and tall) in the same method you plan to knit (flat or in the round). Measure it straight off the needles, and then launder it the way you’ll launder the finished item. After it’s dry, measure it again. Why measure twice? If the gauge changes dramatically after washing you’ll need to take it into account while knitting. Otherwise, the first time you wash your garment it will completely change its shape.
If you’re looking for an easy care garment, many yarns are washable even though they state “hand wash only” on their labels, so this is the time to give it a try. Often I find that a yarn is washable but it loses some length in the process (often as much as 20%). I compensate by adding the length while knitting so the final garment is the right dimensions.
One other note about swatching – please, please do not edge your swatches in garter stitch! They make pretty swatches, but garter stitch has a compressed row gauge and can alter the row gauge on your swatch. The best swatch is one that just uses the stitch you’re swatching. Washing and blocking will help battle the curl of stockinette, and you can always pin in place for measuring.
Similarly, measuring too close to the bound off edge can give you a skewed gauge measurement as well, so a larger swatch is a safer bet.
Once you’ve selected a yarn and you’ve started your project, make sure you listen to your intuition. Check your gauge throughout the project, match it to the schematic, and if something doesn’t seem right, listen to that little voice and consider your options. If I’m concerned about how a piece is coming out, I’ll put it on some waste yarn and wash it to see how the finished piece looks. Often this is enough to give me the confidence that I’m on the right path. And if I’m not, it might be just the excuse I need for another trip to the local yarn store.