What follows was a post I made in the yarn forum on ravelry when someone was asking about fiber types to help them choose yarn for a light summer sweater. Guess I was feeling a bit wordy that day.
Going entirely from rote, so please to have the forgiveness if I miss a micron or fiber type or something…
There are technically 3 kinds of fiber: protein (comes from animals), plant (comes from…well, go ahead and guess), and synthetics. Some plant fibers can be processed as synthetics (i.e. bamboo, seasilk, etc.–they use the “rayon process” where the stuff gets munched up and extruded), but they are still plant fibers.
Protein fibers like wool, alpaca, cashmere, angora, mohair, etc., are the hairs of animals and as such they have some similar properties to human hair. There is a cuticle coating the hair shaft that is comprised of many little scales and the size, shape, and texture of these scales differs based on the type of fiber it is and what critter it comes from. (Some animals have what is called a “double coat” meaning they have longer, straighter, thicker hairs called “guard hairs,” which usually should not be used in processed fiber. Exceptions can be made where the guard hair is barely noticeable, such as in a fiber like angora or where the guard hairs are so fine they feel just as soft as the other fibers in the fleece. Guard hair or “primary fibers” are what the actual coat of the animal or “secondary fibers” grow around. Imagine it like a little hub with a bunch of smaller nodes nestled around it. Guard hairs protect these softer undercoats to keep animals clean, dry, and warm. Some guard hairs are so fine they are practically indistinguishable from the main coat, and some are wiry, thick, coarse, and scratchy. Now that you know about both kinds of fiber you can find on a single animal…)
If you want elasticity and warmth, you can’t beat protein fibers. Since animal fibers are actual hairs they can stretch just like human hair does, and many fiber animals have something called “crimp” which is little kinks or bends in the fiber; these make the fiber kind of like a slinky–very bouncy. Protein fibers are designed to keep animals warm, so they keep people warm too. Some are warmer than others. I feel comfortable saying that a good rule is: the finer the fiber, the warmer it is. The measurement of a fiber’s diameter is called a “micron” and it’s symbol is µ. It’s one millionth of a meter (or 1/25,400th of an inch, whichever helps you understand it better). The smaller the average fiber diameter, or AFD, the finer the fiber. At the finest end you have silk, which is around 5-10µ, then virtually unattainable fibers like shahtoosh and vicuña which can be anywhere from 8-14µ, and come from endangered (yet amazingly ADORABLE animals: the Chiru antelope and the vicuña, respectively). Then you go up a little and get things like guanaco (relative of the vicuña, both of which are members of the camel family), angora, ultra-fine merino, and ultra-fine cashmere at around 10-16µ. Then a little further on, things like alpaca, fine wools, camel, and medium and lower-grades of cashmere, and the wool of the American Romeldale/CVM at approximately 15-25µ. Last, for human wear, medium wools like Corriedale, Bluefaced leicester, as well as mohair, etc. clock in at around 20-30+ microns. Remember the guard hairs from before? Even if the fleece’s AFD is below 30µ, if any fibers in the fleece–usually the guard hairs–are near or above 30µ, you will have what is called “the prickle factor,” which is when a fiber feels itchy. Fibers that go near or over 30µ are uncomfortable for human wear (as a general rule, there may be some iron-skinned person that will chime in with how much they love a sweater they spun and knitted from guard hair, but odds of that are slim).
Some fibers, like those of members from the camelid family, are hollow (also called “medullated” but that word has a different meaning when used on different fibers and can be confusing, so I’ll keep using “hollow” instead). The hollow area traps more air in the fiber making these fibers exceptionally warm. Yarns made from camel, alpaca (there are two breeds: huacayas and suris), guanaco, llama, and vicuña are very warm. All of these fibers, except for Suri alpaca, have pretty good memory. Suri alpaca is a wonderfully drapey fiber and makes for nice warm items that don’t need elasticity. The fibers from camelids are very soft due mainly to how large, flat, and smooth the individual scales on each hair are. They don’t stick up as much as some other fibers, and that smoothness can effect their elasticity, so you do have to allow for that when knitting to maintain the inherent elasticity of the fiber (q.v. my other post about knitting with alpaca).
Wool has great elasticity, really the best, for two reasons: its crimp architecture (especially in the finer wools) meaning how many “zigzags” (not the scientific term!) each hair has, as well as its scale structure. The scales on each wool hair stick up just a little more than on their other animal hair counterparts and this acts almost like velcro to keep wool yarns and garments made from them “in check,” however, it can also be detectable on your skin if you’re touching high-micron fiber. Some people think they are allergic to wool because they encountered some that was itchy, but it could have just had a high micron, unpleasant scale structure, or the fibers could have been damaged in commercial processing resulting in “sticky-uppy” scales that feel scratchy to the touch, even on finer wools.
Angora, cashmere, qiviut, yak, etc. are sumptuous fibers, and incredibly warm, but they really lack elasticity (either because of staple length, scale structure, lack of crimp, or all of the above) and are known for requiring care in working and/or blending with other fibers so as not to sag out of shape.
Both camelid and ovine (sheep) fibers wick away moisture, just like they would on the hoof. By allowing sweat to migrate to the outside of the animal, they keep them nice and toasty warm as well as dry and clean. Protein fibers also “insulate” meaning they trap air to regulate heat (this is different than trapping all air to make one swelter and sweat!) by regulating heat on the animals they come from they help keep their bodies at the right temperature. This means protein fibers are good for year-round wear. These are things that only protein (hair) fibers will do.
Silk is also a protein fiber, but isn’t an animal hair. It is a filament extruded by an animal. It has a lot of elasticity. You can pull and pull and pull and pull on knitted up silk and it will stretch and stretch and stretch unless knitted tightly. The culprit here is that silk has no scales because it’s not a hair; it’s worm barf! :P Silk is very soft and good for folks who might be allergic to other animal fibers, but since it’s heavy and needs to be knitted tightly it would be tough to reach the kind of versatility shown by the animal hair protein fibers. (It wicks away moisture to a degree, but since it’s a heavier fiber it just adds to the weight of the fabric, and well, as you can imagine: contributes to stretching. Silkworms don’t sweat, so it makes sense that silk wouldn’t need to wick moisture well.) If you want something light and slinky, that is still warm and soft, or if you’re allergic to other protein fibers, silk is wonderful.
Plant fibers don’t exist to keep plants warm, and their use in textiles is best-suited to non-insulative items. They can actually do more harm than good since they don’t wick away moisture, but just keep absorbing it, this means they can get pretty wet, which is bad news for insulation. Anyone who has ever been in the Pacific Northwest in the winter can attest humidity just makes cold even more bone-chilling. Plant fibers also lack elasticity since they aren’t composed like a hair and have no need to stretch. They have plenty of uses, but if you want stretch and warmth, best to look at protein fibers.
This brings us to…synthetics. Synthetics can be very warm, and a lot of high end sport clothing is made with super-fine manmade fibers, but for handknitting and crocheting, the space age stuff is non-existent (to my knowledge) and synthetics, like plant fibers, lack the elasticity and moisture-wicking properties of protein fibers. They also don’t insulate: they stifle. By trapping everything–heat as well as moisture, and not absorbing trapped moisture–they tend to make one feel clammy, which is basically the opposite of what you’re seeking. They have their uses, too, but I tend to use them for things that I won’t be wearing since they have unideal properties for garments.
Hopefully this will shed some light on what kinds of fibers you’ll like the best for your project. (Hopefully I haven’t insulted the English language with some hilarious typo, but if so, will try to keep edits to a minimum for clarity’s sake.)
© 2010 Bethany Hendrickson. All rights reserved.