The japanese washcloth is different from the towelling ones we are used to on this side of the world. First, there's the size - the washcloth is a long rectangular shape (the Muji travel washcloth measures 28x95cm), which makes it perfect for washing your back - just grab either end of the cloth and stretch it across your shoulders. You can also fold it up to use it more like a traditional sponge.
The second difference is with the material used. We're used to washcloths made of towelling material, or those nylon showerpuffs. The japanese washcloths are also made of nylon, but very loosely woven, which gives them a slightly rougher feeling. Sounds uncomfortable, but this actually feels really invigorating to use and has a great exfoliating effect - my skin feels much smoother and softer when I use it regularly, and yet it doesn't dry my skin out or irritate it.
The cloths are super easy to wash in the machine too, and the travel version pictured even comes with a handy ziplock pouch, making it perfect for travelling with. Get your japanese washcloth from Muji stores or for around €5 for the travel version and slightly more for the full-size versions.