Cultivate the silkworms on mulberry leaves. Silkworms spin cocoons. Once they are fully formed, you can boil the cocoons, killing the pupae inside and dissolving the glues binding the silk together. Each cocoon is made up of one extremely long strand. You can twist several of these very fine threads together to produce the desired diameter of raw silk. This silk is reeled into skeins and packed into small bundles called books. In this form raw silk is shipped to silk mills all over the world.