Thursday, April 18, 2013

Tips From the Knit Doctor - Fibers



          Yarn fibers can be divided into three broad categories: animal, plant, and synthetic.  Which you use depends on what properties you’re looking for in your knitting.

            Wool and alpaca are animal hair fibers. They are very warm, and can absorb up to 30% their weight in water while still feeling warm and dry to the skin. They are naturally flame-retardant, strong, elastic (which means they can not only stretch, but can then rebound back to their original size), and block beautifully (which means you can stretch them to size, and tension irregularities tend to even out). Merino wool and baby alpaca are the softest, but at the cost of durability. Wool and alpaca can be blended with other types of fibers for additional properties, such as nylon for strength, silk for shine and drape, and cotton for coolness. 

            Animal hair fibers can be felted, since their fibers have microscopic scales which can cling together. Superwash wool has had its scales removed, so it can be machine washed without felting. Without the scales to hold adjacent fibers together, however, the wool loses its elasticity and can stretch irreversibly out of shape, so is not good for large heavy garments that can stretch under their own weight, but is great for socks, which can otherwise felt through abrasion in the warm, moist environment of a closed shoe.

            Silk is another animal fiber (but is not hair), extruded by silkworms in long filaments. It has a wonderful shiny luster and good drape. Like wool, it is a good insulator and can absorb and release moisture, feeling warm when wet, and is strong. It is not elastic, however, so it can stretch out of shape. It is smooth and slippery, good for lace shawls and slinky tops; if more body is desired, a blend with wool will yield better results.

            Cotton, a plant fiber, is the world’s most used fiber. It has excellent water absorption and dries quickly, making it comfortable to wear in hot weather. It is strong and non-allergenic. It can be obtained as loosely spun yarn, which is soft but not very durable, or it can be mercerized, a treatment that makes it smoother, stronger and shinier with less shrinkage, resulting in a cooler, less insulating fabric. However, it is not elastic, and so garments made of cotton, which can be quite heavy, can stretch irreversibly under their own weight; also, necklines and ribbing won’t stretch and rebound like those done in wool. Good patterns already take this into account, but realize that if you substitute cotton for wool in a pattern, the garment won’t behave the same. Tension irregularities also show readily in cotton. Cotton can be blended with other fibers for more elasticity or less weight.

            Linen comes from the flax plant. It feels like rough twine at first, but the more it is worked and washed, the softer it becomes. It breathes well; like cotton, it absorbs moisture and wicks it away from the skin, making it comfortable in warm climates, and also like cotton, it has no elasticity, but it does drape well. 

            Acrylic is a synthetic that is made as filaments which can be spun into yarn. Acrylic yarn is fine and soft, and of all the synthetics, is the most similar to wool in look and feel. It has some positive qualities: it is inexpensive, can be machine-washed, doesn’t stretch, is impervious to moths and mildew, does not felt or shrink, is quick-drying, and can be added to natural fibers in small amounts to make them lighter, stronger, and machine-washable. But it doesn’t insulate the way wool does, it pills badly, and it melts at high temperatures rather than burning and in a fire will create chemical burns on skin, so it is not appropriate for sleepwear for babies. It also cannot be blocked to shape the way wool can, and tension irregularities show. It makes warm afghans that are not as heavy as wool ones, but that can give you static electricity shocks in dry winter air.

            Hopefully this short summary of fibers will help you choose appropriate yarns for your projects. For more detailed information, I recommend Clara Parkes’ book, The Knitters Book of Yarn.