It's a disposable box that costs about 10 or 20 dollars a box. There is some chemical stuff underneath the rice, and when the rope is pulled, the lunchbox heats up on its own. You don't have to plug it in. This thing is rare. Taobao sells all the lunch boxes. Only ate once is in Guangzhou Shaba toll station near a convenience store. Supermarkets I have looked for not sold.