They cost a fair bit, but they're completely worth it, considering you never buy cleaning products anymore, and they last forever.

It's a fine microfibre, so it sucks all the dirt and germs up as it absorbs the water. You can feel added resistance on a dirtier surface as it works to pick up the junk. After mopping (or wiping, if you use the mitts) you put them in a special care bag, and wash it. That's where the bacteria goes.