Let's face it, there are hundreds of lace yarns out there to choose from, all the way from cheap wools that break as soon as look at them to ultra silky blends of silk and mohair, alpaca and pure mulberry silk.
So how do you select the yarn that is right for your next project?
Quality counts. Lace knitting is a significant amount of work and the last thing you need is to spend a few weeks working with a yarn that you don't enjoy working with. Is it worth saving $10 on your project when the result is a less than satisfying experience and an even less gratifying finished project?
Choose the right fiber. Know your fibers. For a start there is no point knitting a beautiful shawl in cheap acrylic yarn and then finding out it cannot be blocked. I have seen it done. Don't do it! Okay let's assume you aren't quite that naive and you want to know whether to use a nice wool, cotton, silk or bamboo or a blend of one of those. For this purpose let's assume that pretty much all animal fibers have similar qualities.
DRAPE: The first thing to think about is drape. This is how a garment hangs when you wear it. If you are making socks you don't want much drape, this would make them fall down. More drape means less "bulk", the more drape a fabric has the more it will conform to your shape and hang down. The less drape the more it will fluff out and ride up. Silk has probably the most drape, followed by bamboo, cotton and then animal fibers. A loose spun yarn will also have more drape than a tightly spun yarn, a finer yarn will have more drape than a thicker yarn. Generally a shawl, summer scarf or summer top will want to be knit with a yarn with plenty of drape, a winter scarf, winter top or jacket will want less drape.
Related to drape is a property most often refered to as "hand". This is how a yarn (before but more usualy after being knit) feels when you feel it. Most people prefer a soft hand on lace garments. Two factors influence the hand of a fiber, the softness and the silkyness. Wools that felt or are made from thick fibers generally have a coarser hand, finer yarns generally have a softer hand. The "hands down" winner, excuse the pun, is a high quality mulberry silk, such as Ivy Brambles Pure Silk. This yarn is spot on lace weight at 1000 meters per 100 grams, and one skein is usually enough for most medium size shawls.
For wool it is hard to beat cashmere for hand and softness, but at a price. Cashmere, like many wools is also not especially strong, can sometimes felt or tangle on the skein and might break at lace weights. This is an important factor in choosing a wool to work with. The strongest and easiest to use wool for lace work is probably merino which has a long staple length making it very strong. The only downside is that merino wool felts easily meaning you had better be careful when you block it and not wear it out in damp weather. The solution? Ivy Brambles has a 100% Superwash Merino lace weight called Romantica. This is made from exception fine quality merino wool treatd to prevent felting. It has a super soft hand, blocks incredibly easily, and does not pill, break or tangle when you work with it. It is so soft it rivals cashmere at a fraction of the cost!
The last thing to think about when choosing a yarn for a lace project is how fuzzy it will be. Mohair blends are probably the most fuzzy, cashmere is soft but also can be fuzzy, some other wools, especially poorly spun wools, can also be on the fuzzy side. If your pattern is intricate and you spent a lot of time knitting it, you might not want to choose a fuzzy yarn that will tend to hide all that work.
Best advice - before you substitute a yarn see a sample of that yarn knit up in a similar garment, make sure it blocks, and make sure you will enjoy working with it!