All cotton weaving yarn, heavy string type carpet warp, probably old Mayville thread. This is a lot in a rainbow of colors!
There's 30+ spools (4" tall) some full, many partially or mostly used. The whole lot is shown all together in the first photo.
These have been stored away for many years, and the outer wraps are very discolored, spotted and dusty. The thread is very strong and supple, though. And these old heavy cardboard spools make great primitive display pieces!