Denim is made from cotton. It is a woven twill weave fabric popular for its comfort and durability. The twill weave gives the denim its recognizable diagonal pattern.
Regular blue denim is made with both blue and white fibers. The pattern is called the twill weave and the weave can either be left hand twill or right hand twill. Many historians believe that denim has been around since the Middle Ages and the word "denim" came from the French term "serge de Nimes."
The types of denim most people are familiar with comes from the way the fabric is treated. For example, stonewashed denim gets its distinctive look when it is washed using pumice stones, ceramic balls, enzymes or sand.