I use cottons when I can or the others. Prefer cottons most of the time. In mixing the two, cotton and say a poly or poly/cotton blend, it looks different than the cotton after washing. If that doesn't bother you have fun and go for it. The cotton usually will be a little wrinkly where as the poly and blends look like they may have been ironed. Otherwise you can mix most anything. Washing first would be good.