In truth, the type of project determines the type of yarn. Ragg yarn, a thick yarn made from one ply of shoddy and two plies of wool, makes a great warm sock but a terrible lace tablecloth. Cobweb Shetland makes a flimsy Aran sweater but is perfect for an heirloom shawl. Wool will drive an allergic person to distraction but some people hate the feel of acrylics. Some natural fibers will felt and become weatherproof; others are poor insulation.

Fiber:

the strings and filaments of which yarn is made.

Yarn:

fibers processed into a strand long enough to work.

Whatever the yarn is worked into is fabric, whether it is woven, knit, crocheted or processed by another method.

Ply:

Most yarn is made of plied material. A ply is a twisted strand. If the twist is a firm one, the yarn will be fine; if is too firm, the yarn "kinks." If the twist is loose, the yarn is soft, thick and a bit less hardy.

The number of plies in yarn has nothing to do with thickness. A yarn made of four firm plies may be thinner than one made of two loose ones. That having been said, yarn strength and evenness depends on the number of plies. Yarn is usually plied (the act of twisting the twisted strand together) in the opposite direction of the individual strands. This corrects the tendency of the yarn to slant as it is worked. A sweater made from a firm, multi-ply yarn knit with a small gauge might survive generations of wearers.

Unplied yarn is a hunk of wool that has been stretched out a little. Roving, a fluffy bulky yarn with no twist, is an example of this. Sweaters made of roving are fragile and tend to pill.

Weight:

Yarn comes in fine, medium and heavy. Fine is often referred to as 'fingering' or baby yarn. 'Sport' or 'jumper-weight' yarn is thicker than fingering.

Extra-fine yarns are used in lace-knitting. Some of these are spun as thin as a human hair. A shawl made of this wool might weigh only two ounces but contain 6,000 yards of yarn.

"Worsted" is the term used for what most people think of as sweater yarn but worsted is actually the term for a yarn whose fibers were combed before spinning. This sweater name is more properly called 'double-knitting' in England and 'Germantown' in America.

Heavy yarns are thick ones meant for large needles. Bulky and chunky are synonyms.

Virgin and other terms:

Virgin fiber is fiber that has not been knit, woven or worked beforehand.

Shoddy is yarn or fabric made from scraps; obviously, it has been worked beforehand. Since it does not wear well, its name is used to describe anything poorly made.

Felt is what happens when wool shrinks and mats together; the action is usually irreversible.

Pills are little matted balls that form on sweaters. They happen as the soft yarn rubs against itself and the fibers tangle.

Knit-alongs are yarns knit with the main yarn in a fabric. They do not affect the gauge of the pattern but add strength, color or pizzazz.

Gauge is not a fiber term. It is the number of stitches per inch the yarn gives when knitted. Although the size of the yarn is a factor, needle or hook size and the tightness with which the yarn is worked also determine gauge. [Editor's note: "gauge" is known as tension in the UK.]

Hand is how a yarn feels.

Before spinning, the fiber is cleaned, untangled and carded (brushed smooth and straight.) Some fiber are also combed, which further straightens them and sorts them by length. Bundles of these fibers are drawn slightly into 'slivers;' if they have a slight twist to them, they are called roving. Fibers are pulled from the roving and twisted into plies. Twisting these plies together produces different weights and types of yarn.

• Wool as far as I'm concerned (and I'm the one writing this FAQ,) wool is fiber from a domesticated sheep. Wool accepts dye well, is flame-retardant by nature, remains warm even when wet, sheds water better than other yarns. Natural wool should be hand-washed. 'Superwash' wool has been treated to allow machine washing. Wool will usually resume its proper shape when washed correctly; if it is mistreated and washed in too-hot water, it will shrink or felt.

• Mohair is fiber from an Angora goat. Mohair is durable, sheds dirt, dyes well and does not felt easily. Despite its hardiness, it is usually spun into yarn used for fluffy garments and scarves. This yarn is abraded, roughing its fibers to create that 'fuzzy' look.

• Angorais fiber from rabbits. Fabric made from this yarn is inelastic (no stretch), very fluffy, soft and warm. Contrary to a belief popular in the 1950s, a Angora sweater does not increase the size of one's bust.

• Silk is the fiber produced by silk moths. Silk knitting yarn is made from damaged silk cocoons and broken fibers. 'Raw' silk still has the original moth secretions in it. 'Tussah,' silk obtained from wild moths is brown. The food fed to domesticated moths determines their silk's natural color; this can white, green or yellow.

  Silk retains heat, absorbs moisture, pills less than wool, is very strong and very stable when knit, neither shrinking or stretching.

• Cashmere is fiber from the undercoat of a Cashmere goat. It is so expensive because only a few ounces are obtained from each goat per year. It is such a delicate yarn, more fragile than wool and more susceptible to abrasion, that it is usually blended with wool to make it more durable.

• Camel is fiber from the two-humped or Bactrian camel. Camel hair cannot be bleached, so it is either used undyed or dyed a darker color. It is lightweight and fragile.

• Vicuna comes from the vicuna, a South American relative of the camel. They are rounded up once a year and shorn like llamas or sheep; their hair is finer than any other animal fiber.

• Alpaca is a smaller relative of the llama but its hair is more commercially valuable. Yarn from this fiber does not felt or pill easily. It comes in fifteen natural colors (as do the alpacas) and is denser than wool, so fabric knit from it may droop. The undercoat of a llama is very similar to alpaca hair.

  Two places on the Web to find out more about alpaca are AlpacaNet and Chase Tavern Farm Alpacas.

• Qiviut(kiv-ee-uht) is included here because it is a wonderful Scrabble word; the fiber itself is very hard to find. It comes from a musk ox and resembles pale gray cashmere but does not shrink.

Vegetable fibers:

• Cottonis the fiber surrounding the seeds in a cotton pod. Usually white but there are green and brown varieties. Cotton is heavy, dense and inelastic; although it will regain its shape after washing, its ability to do so decreases over time. It is comfortable to wear in a cool climate but not a hot one (the opposite of wool) and is slow to dry once wetted. It makes a weaker yarn than silk or linen but is stronger than wool.

• Linen comes from the flax plant. It is durable and stronger than any other fiber. Fabric made from it becomes softer and more beautiful with age. It absorbs moisture better than cotton and dries more quickly, making it more comfortable to wear than cotton in hot temperatures. It is easier to wash than wool and does not stretch or shrink.

• Ramie is made from nettles (as in the Fairy Tale "The Swan Princes," where their sister had to gather nettles and spin them into yarn.) It is often used as a substitute for linen since it is less expensive but shares linen's good qualities.

• Rayon is a fiber produced from natural ingredients by artificial means. Cellulose from wood pulp or cotton is treated chemically until it may be drawn into filaments. Rayon is a weak fiber but it is absorbent, dries quickly, and stretches (although it does recover some when dried in a automatic dryer.)

Synthetic fibers:

• Nylon is lightweight, strong, elastic, resists abrasion, does not stretch or shrink (except at high temperatures,) and is easy to wash. It is usually combined with wool to impart its strength and elasticity to the wool. Pure nylon is available as a 'knit-along' to strengthen sections of a garment that will encounter wear, such as elbows and sock heels.

• Polyester is the most common type of synthetic fiber. Fabric made from it retains its shape. It adds strength and resilience to natural fibers. Polyester is very easy to wash and is more comfortable to wear than many other synthetics.

• Acrylics are the most common synthetics in knitting yarns. They are resilient, moderately strong, somewhat inelastic, feel good to the hand and are light in weight. Acrylics are easily made to imitate natural fibers so they are sold as alternatives to wool. However, acrylics cannot wick away moisture from the body so their warmth diminishes when wet. The fiber burns readily unless treated and will shrink in moist heat. Acrylics are often used to achieve novel textures and characteristics that are not available with natural fibers.

• Metallics (described above) are best used as a 'knit-along' with another, stronger yarn.

The length and quality of the fiber in a yarn determines its texture, luster, strength and hand. Yarn made from long fibers will pill less, be smoother, stronger, more lustrous and more elastic. Yarns containing a mixture of fiber lengths are softer, fuzzier and less strong. Tightly twisted yarns display the texture of a knitted pattern to its best advantage. Fuzzy yarns obscure a stitch pattern but are warmer and cozier, although they wear less well and often shed like a St. Bernard in a Georgia summer.

'Novelty' yarns are ones with an unusual texture, color or appearance that comes through differences in its ply sizes, the combinations of its fibers or some variation in its spinning.

Slub yarn has a textured, lumpy surface. It has a smooth ply and one that was spun unevenly, which creates 'slubs' or lumps in the ply. Crepe yarn has tiny bumps. Boucl&ea; yarn has its smooth ply so tightly twisted that it curls around the slub ply.

Roving, mentioned above, is loosely spun wool. It is a weak yarn and can pull apart while being knit. Once made up, the fabric itself holds the fibers together; although warm, the fabric will pill, abrade and does not wear well.

'Eyelash' or 'fur' yarn has long filaments grouped along its length. When the yarn is knitted, these filaments stick out from the fabric and give it a furry look.

The following are not yarn but can be knit like yarn.

• Chenille is cut from a specially woven fabric. It twists while being knit because it has no oppositely-twisted plies to counteract the twist imparted by the knitting. It sheds from its cut edges.

• Ribbon yarn is just that: thin ribbon used for knitting. Although most knitters let the yarn twist as it may, fine ribbon-knitting keeps each stitch as flat and smooth as possible.

• Strips of fur -- see chenille

• Leather thongs -- see ribbon yarn

• Crochet cotton, string and rope

• Anything else that can be wrapped around a needle or hook.