Details: People soon began to develop and maintain herds of wool-bearing animals. The wool of sheep was soon recognized as one of the most practical to use. During the eleventh and twelfth centuries, wool trade prospered. The English had become proficient in the raising of sheep, while the Flemish had developed the skills for processing. As a result, the British began to sell their wool to the Flemish, who processed the raw material and then sold it back to the English. Wool is produced by follicles which are small cells located in the skin. These follicles are located in the upper layer of the skin called the epidermis and push down into the second skin layer called the dermis as the wool fibers grow. Follicles can be classed as either primary or secondary follicles. Primary follicles produce three types of fiber: kemp, medullated fibers, and true wool fibers. Secondary follicles only produce true wool fibers. Medullated fibers share nearly identical characteristics to hair and are long but lack crimp and elasticity