When I write about yarn design and when I record the final statistics of my finished yarns, I use specific drafting terms to describe how the yarns are made. I wanted to make sure I added these terms to my glossary:
Drafting: The method of how fiber is pulled out from the fiber supply and presented to the twist, which enters the fiber to form yarn. There are two main yarn families based on drafting method: worsted and woolen. Drafting fiber is one key component of yarn design, as it determines the size (diameter) of the yarn and also strongly influences yarn characteristics such as luster (shine vs. matte), loft (dense vs. airy), elasticity (drape vs. stretchiness), strength, resistance to abrasion, stitch definition, and surface texture (smooth vs. fuzzy).
Worsted: Worsted yarns are always made from a combed top fiber preparation. Creating combed top removes all short and weak fibers, leaving only the longer and strong fibers that are aligned parallel with each other. The most traditional, "pure" worsted yarns only use fibers that are at least 3 inches or longer with 7 crimps or less per inch. In worsted drafting, twist enters attenuated fibers and does not enter the fiber supply. This means that twist enters fibers that have been straightened and held under pressure, therefore the fibers in the yarn are locked into place by the twist and cannot shift sideways. This structure empasizes shine, drape, strength, and smoothness of the fiber. It is a denser yarn, since the drafting method compresses air out of the yarn as twist enters the attenuated fiber. These yarns are not terribly elastic, but they resist abrasion with excellent durability and have crisp stitch definition.
Semiworsted: This drafting method uses worsted drafting with any fiber preparation, not just combed long fibers. Twist is not allowed into the fiber supply. A semiworsted yarn will be more like worsted than woolen yarns, but it will be different from traditional worsted yarns by having more loft and elasticity with a fuzzier surface texture. They will still have more drape and stitch definition compared to woolen and semiwoolen yarns.
Woolen: Woolen yarns are always made from carded fibers that are short (less than 3 inches) and highly crimped (more than 7 crimps per inch). Carded fiber does not line up fibers in a parallel formation, and can have fibers of different lengths in the preparation. In woolen drafting, twist is used as part of the drafting process and enters the fiber supply. This means the fibers are not perfectly aligned next to each other within the yarn, but can move sideways. This structure emphasizes loft, stretch, and elasticity with a matte, fuzzy surface of the yarn. Woolen yarns are not as durable or resistant to abrasion as worsted yarns, but they are lightweight & airy, with lots of stretchiness, having an almost spongy texture. They do not have crisp stitch defintion, but have a soft blurring effect on stitches and colors in a pattern.
Semiwoolen: This drafting method uses woolen style drafting with any fiber preparation, not just carded short fibers. Twist is allowed into the fiber supply as fibers are drafted. Semiwoolen yarns will lean towards woolen characteristics on the yarn spectrum, usually having lots of elasticity and will feel very lofty compared to a worsted yarn, but they can have more shine and stitch definition than what is typically seen in woolen yarns.