Well, you *can*, but the minute it gets
wet damp, even just from body precipitation, it starts to be worse than wearing nothing, as far as keeping you warm/protected. So it's not a good idea unless it's super hot out. And it's never super hot out when & where I go camping
I forget the exact numbers, but it will hold its own weight in water quite a few times over, but not hold it in a good way, hold it in a "leech you of all body heat" way. (Wool will hold water in a good way, I don't know how, but it just adds to its insulating properties. Nylon, silk, etc are all pretty neutral)
So cotton is really great for cooling someone down when they have heat stroke, but for going camping... not so much.