For the inside of notebooks it is most common to use offset paper, to easily allow notes or drawings on the surface.
The weight to be used for the inside paper varies depending on the type of notebook. In notebooks, it can be an offset from 80 to 120 grams.
For sketch books the weights are usually higher, even reaching 300 or 350 g in order to better withstand watercolours or inks to paint without wrinkling or damaging the surface of the paper.
Notebook covers can be printed on any existing material and weight on the market, the possibilities are unlimited, although the most common are:
Coated, offset, recycled, card and various specialities. It is even common to protect the covers by printing them on rigid, PVC or polypropylene media.
Even printing on them.