Here is a guide to string mopheads.
Cotton mopheads are very absorbent and work well for cleaning water on hard floors (tile, wood, concrete, etc.).
Rayon mopheads are stronger and release liquids more effectively. They work very well for applying finishes and using harsh cleaning products.
Synthetic mopheads are very strong and so they are a good choice in cleaning rough surfaces.
Blended mopheads (rayond and polyester and sometimes cotton) are the most durable. They are multipurpose tools.