These are sold as blotter in sheets already washed and boiled. Papers such as Stonehenge and Lenox 100 are made of cotton linter. They are reasonably priced papers and are suitable for students who do not wish to spend much and still want archival quality. These drawing papers make it harder to fully erase dry media and they have a limited ability for color and tones. In printmaking they are great proofing papers, but wouldn't be my choice for printing an edition as they do not deliver a full range of values and detail.
Cotton rag comes from the part of the cotton plant that is used for textile manufacture.
The fibers used for threads are longer and tougher than cotton linter. The paper maker undoes all the mesh process of weaving and frees the fibers from the tougher cell surface which makes for stronger paper. I have heard that recently the distinction between linter and rag has become loosely defined in most catalogs. Indian papers are primarily made from khadda, unbleached hand-spun rag left over from the garment industry. The cotton and hemp rag along with gelatin or wheat startch sizing give these papers their exceptional strength.