Cotton and blendsJeans, once called bluejeans, are most closely associated with denim, a course, twilled cloth made of cotton, not wool. Wool is rarely found on the content label of jeans.

 

 And the answer is: CottonJeans are made of cotton. Some jeans will add some spandex or Lycra (R) to add some stretch to it. Now if we wanted to discuss what sort of cottons are used in jeans, that’s a whole separate article. So yes. Cotton. and Spandex

In a word, jeans are made of denims.And denims are made of cottons.
I know these because I work in jeans factory.

 Refer:http://www.jeansfactorys.com/FAQ/What-is-jeans-made-of.html