Yarn is a continuous fiber that is used to construct a fabric. It is usually made from several natural or synthetic strands, called plies, which are spun together into one single strand. Most yarns are 4-ply, meaning they are made from four strands. They are normally sold by weight (in ounces) in balls called skeins, although some novelty yarns and crochet cotton can be bought by the spool.
The thickness of the yarn is graded from 1 to 6 by the Craft Yarn Council of America. The bulkiest yarns are graded 5-6, and are usually reserved for bulky winter wear or rugs. Medium-weight (also known as sport-weight or worsted-weight) yarns are graded 3-4, and are the general all-purpose yarn used for most projects. The finest yarns are 1-2, and work well for lacy projects and baby apparel. And even thinner than the finest yarns is crochet cotton, which is used for making crochet lace. Crochet cotton has its own grading system and is graded by weight; for example, #3 or #10. The larger the number, the finer the thread.
In addition to the standard wool-type yarns, “novelty” type yarns have recently come into popularity. Bouclé yarns are made by spinning one of the plies at a different tension than the rest, thus giving the yarn a rough texture. Eyelash yarns have short strands of fiber sprouting from the main thread, and give a hairy or furry appearance to the finished project. Ribbon yarns give the appearance of ribbon, but are more elastic than normal craft and sewing ribbon.
The typical worsted-weight, 4-ply yarn is the best to use when first learning to crochet, but once the basics have been mastered, it’s fun to experiment with different types of yarn to see the different effects they create.