Why do some sandpapers need water when in use?

Why do some sandpapers need to add water when they're being used?
Especially the water sandpapers. This kind of sandpaper works better in a wet environment. Adding water has a few main advantages. One is that it can cool things down and prevent the material or the sandpaper itself from getting damaged because of too much heat from the friction. Another one is that it makes the debris come out easier, keeps the sandpaper's grinding efficiency, and stops the debris from blocking the spaces between the grains, so the grinding quality won't be affected. The third one is that it makes the grinding more efficient. When it's wet, the debris can go away with the water more easily and the grinding process is smoother.

When you're using it, if it's a small thing, just put it in water and use the sandpaper to grind. For big things or things that can't be soaked in water easily, you can use a coarser sandpaper to do the initial grinding first, then change to the water sandpaper and add water while grinding. When there's less water or it dries up, add some in time to make sure the grinding effect is good.

But you need to know that water sandpaper shouldn't be used for dry grinding. Otherwise, its performance will be affected. At the same time, start with the fine-grit sandpaper and then move to the coarser grit gradually. This way, you can get a better polishing effect.

All in all, adding water when using sandpaper is to make the grinding process better, improve the efficiency and the quality.