Yarn types refer to the various categories of yarn used in knitting and crocheting, each with unique characteristics. Common types include acrylic, wool, cotton, and blends. Acrylic yarn is affordable and easy to care for, while wool offers warmth and elasticity. Cotton yarn is breathable and ideal for summer projects. Yarn can also be classified by its thickness or weight, such as fingering, worsted, and bulky. Fingering yarn is very thin, suitable for delicate projects, while bulky yarn is thicker and works up quickly, making it great for cozy items. Understanding these types helps crafters choose the right yarn for their projects.